linux终端设备uart驱动分析

傷城~ 2022-07-12 07:50 209阅读 0赞

文章来源：[http://blog.chinaunix.net/u3/94284/showart\_1982227.html][http_blog.chinaunix.net_u3_94284_showart_1982227.html]

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           <span style="font-size: small;">一:前言</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">接着前面的终端控制台分析,接下来分析serial的驱动.在linux中,serial也对应着终端,通常被称为串口终端.在shell上,我们看到的/dev/ttyS*就是串口终端所对应的设备节点.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在分析具体的serial驱动之前.有必要先分析uart驱动架构.uart是Universal Asynchronous Receiver and Transmitter的缩写.翻译成中文即为”通用异步收发器”.它是串口设备驱动的封装层.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">二:uart驱动架构概貌</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">如下图所示:</span> 
          </div> 
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            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <img src="http://hi.csdn.net/attachment/201004/25/0_1272201939ymx9.gif" alt="">&nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">上图中红色部份标识即为uart部份的操作.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">从上图可以看到,uart设备是继tty_driver的又一层封装.实际上uart_driver就是对应tty_driver.在它的操作函数中,将操作转入uart_port.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在写操作的时候,先将数据放入一个叫做circ_buf的环形缓存区.然后uart_port从缓存区中取数据,将其写入到串口设备中.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">当uart_port从serial设备接收到数据时,会将设备放入对应line discipline的缓存区中.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">这样.用户在编写串口驱动的时候,只先要注册一个uart_driver.它的主要作用是定义设备节点号.然后将对设备的各项操作封装在uart_port.驱动工程师没必要关心上层的流程,只需按硬件规范将uart_port中的接口函数完成就可以了.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">三:uart驱动中重要的数据结构及其关联</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">我们可以自己考虑下,基于上面的架构代码应该要怎么写.首先考虑以下几点:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">1: 一个uart_driver通常会注册一段设备号.即在用户空间会看到uart_driver对应有多个设备节点.例如:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">/dev/ttyS0&nbsp; /dev/ttyS1</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">每个设备节点是对应一个具体硬件的,从上面的架构来看,每个设备文件应该对应一个uart_port.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">也就是说:uart_device怎么同多个uart_port关系起来?怎么去区分操作的是哪一个设备文件?</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">2:每个uart_port对应一个circ_buf,所以uart_port必须要和这个缓存区关系起来</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">回忆tty驱动架构中.tty_driver有一个叫成员指向一个数组,即tty-&gt;ttys.每个设备文件对应设数组中的一项.而这个数组所代码的数据结构为tty_struct. 相应的tty_struct会将tty_driver和ldisc关联起来.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">那在uart驱动中,是否也可用相同的方式来处理呢?</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">将uart驱动常用的数据结构表示如下:</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
           <img src="http://hi.csdn.net/attachment/201004/25/0_1272201991pMzB.gif" alt=""> 
          </div> 
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            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">结合上面提出的疑问.可以很清楚的看懂这些结构的设计.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">四:uart_driver的注册操作</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">Uart_driver注册对应的函数为: uart_register_driver()代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">int uart_register_driver(struct uart_driver *drv)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct tty_driver *normal = NULL;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int i, retval;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; BUG_ON(drv-&gt;state);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Maybe we should be using a slab cache for this, especially if</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* we have a large number of ports to handle.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; drv-&gt;state = kzalloc(sizeof(struct uart_state) * drv-&gt;nr, GFP_KERNEL);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; retval = -ENOMEM;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!drv-&gt;state)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto out;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal&nbsp; = alloc_tty_driver(drv-&gt;nr);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!normal)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto out;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; drv-&gt;tty_driver = normal;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;owner&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = drv-&gt;owner;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;driver_name&nbsp;&nbsp;&nbsp; = drv-&gt;driver_name;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;name&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = drv-&gt;dev_name;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;major&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = drv-&gt;major;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;minor_start&nbsp;&nbsp;&nbsp; = drv-&gt;minor;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;type&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = TTY_DRIVER_TYPE_SERIAL;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;subtype&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = SERIAL_TYPE_NORMAL;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;init_termios&nbsp;&nbsp; = tty_std_termios;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;init_termios.c_ispeed = normal-&gt;init_termios.c_ospeed = 9600;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;flags&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; normal-&gt;driver_state&nbsp;&nbsp;&nbsp; = drv;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; tty_set_operations(normal, &amp;uart_ops);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Initialise the UART state(s).</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; for (i = 0; i &lt; drv-&gt;nr; i++) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state = drv-&gt;state + i;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;close_delay&nbsp;&nbsp;&nbsp;&nbsp; = 500;&nbsp;&nbsp;&nbsp; /* .5 seconds */</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;closing_wait&nbsp;&nbsp;&nbsp; = 30000;&nbsp; /* 30 seconds */</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; mutex_init(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; retval = tty_register_driver(normal);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;out:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (retval &lt; 0) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; put_tty_driver(normal);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; kfree(drv-&gt;state);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return retval;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">从上面代码可以看出.uart_driver中很多数据结构其实就是tty_driver中的.将数据转换为tty_driver之后,注册tty_driver.然后初始化uart_driver-&gt;state的存储空间.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">这样,就会注册uart_driver-&gt;nr个设备节点.主设备号为uart_driver-&gt; major. 开始的次设备号为uart_driver-&gt; minor.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">值得注意的是.在这里将tty_driver的操作集统一设为了uart_ops.其次,在tty_driver-&gt; driver_state保存了这个uart_driver.这样做是为了在用户空间对设备文件的操作时,很容易转到对应的uart_driver.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">另外:tty_driver的flags成员值为: TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV.里面包含有TTY_DRIVER_DYNAMIC_DEV标志.结合之前对tty的分析.如果包含有这个标志,是不会在初始化的时候去注册device.也就是说在/dev/下没有动态生成结点(如果是/dev下静态创建了这个结点就另当别论了^_^).</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">流程图如下:</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <img src="http://hi.csdn.net/attachment/201004/25/0_1272202271X4N1.gif" alt="">&nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">五: uart_add_one_port()操作</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在前面提到.在对uart设备文件过程中.会将操作转换到对应的port上,这个port跟uart_driver是怎么关联起来的呢?这就是uart_add_ont_port()的主要工作了.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">顾名思义,这个函数是在uart_driver增加一个port.代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int ret = 0;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct device *tty_dev;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; BUG_ON(in_interrupt());</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (port-&gt;line &gt;= drv-&gt;nr)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return -EINVAL;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state = drv-&gt;state + port-&gt;line;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_lock(&amp;port_mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_lock(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (state-&gt;port) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ret = -EINVAL;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto out;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;port = port;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;pm_state = -1;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; port-&gt;cons = drv-&gt;cons;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; port-&gt;info = state-&gt;info;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* If this port is a console, then the spinlock is already</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* initialised.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!(uart_console(port) &amp;&amp; (port-&gt;cons-&gt;flags &amp; CON_ENABLED))) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; spin_lock_init(&amp;port-&gt;lock);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lockdep_set_class(&amp;port-&gt;lock, &amp;port_lock_key);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; uart_configure_port(drv, state, port);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Register the port whether it's detected or not.&nbsp; This allows</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* setserial to be used to alter this ports parameters.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; tty_dev = tty_register_device(drv-&gt;tty_driver, port-&gt;line, port-&gt;dev);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (likely(!IS_ERR(tty_dev))) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; device_can_wakeup(tty_dev) = 1;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; device_set_wakeup_enable(tty_dev, 0);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; } else</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; printk(KERN_ERR "Cannot register tty device on line %d/n",</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; port-&gt;line);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Ensure UPF_DEAD is not set.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; port-&gt;flags &amp;= ~UPF_DEAD;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;out:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_unlock(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_unlock(&amp;port_mutex);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return ret;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">首先这个函数不能在中断环境中使用. Uart_port-&gt;line就是对uart设备文件序号.它对应的也就是uart_driver-&gt;state数组中的uart_port-&gt;line项.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">它主要初始化对应uart_driver-&gt;state项.接着调用uart_configure_port()进行port的自动配置.然后注册tty_device.如果用户空间运行了udev或者已经配置好了hotplug.就会在/dev下自动生成设备文件了.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">操作流程图如下所示:</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
           <img src="http://hi.csdn.net/attachment/201004/25/0_1272202306Za3V.gif" alt=""> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">六:设备节点的open操作</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在用户空间执行open操作的时候,就会执行uart_ops-&gt;open. Uart_ops的定义如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static const struct tty_operations uart_ops = { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .open&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_open,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .close&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_close,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .write&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_write,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .put_char = uart_put_char,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .flush_chars&nbsp; = uart_flush_chars,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .write_room&nbsp;&nbsp; = uart_write_room,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .chars_in_buffer= uart_chars_in_buffer,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .flush_buffer = uart_flush_buffer,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .ioctl&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_ioctl,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .throttle = uart_throttle,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .unthrottle&nbsp;&nbsp; = uart_unthrottle,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .send_xchar&nbsp;&nbsp; = uart_send_xchar,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .set_termios&nbsp; = uart_set_termios,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .stop&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_stop,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .start&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_start,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .hangup&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = uart_hangup,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .break_ctl&nbsp;&nbsp;&nbsp; = uart_break_ctl,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .wait_until_sent= uart_wait_until_sent,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">#ifdef CONFIG_PROC_FS</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .read_proc&nbsp;&nbsp;&nbsp; = uart_read_proc,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">#endif</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .tiocmget = uart_tiocmget,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; .tiocmset = uart_tiocmset,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">};</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">对应open的操作接口为uart_open.代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static int uart_open(struct tty_struct *tty, struct file *filp)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_driver *drv = (struct uart_driver *)tty-&gt;driver-&gt;driver_state;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int retval, line = tty-&gt;index;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; BUG_ON(!kernel_locked());</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; pr_debug("uart_open(%d) called/n", line);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* tty-&gt;driver-&gt;num won't change, so we won't fail here with</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* tty-&gt;driver_data set to something non-NULL (and therefore</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* we won't get caught by uart_close()).</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; retval = -ENODEV;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (line &gt;= tty-&gt;driver-&gt;num)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto fail;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* We take the semaphore inside uart_get to guarantee that we won't</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* be re-entered while allocating the info structure, or while we</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* request any IRQs that the driver may need.&nbsp; This also has the nice</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* side-effect that it delays the action of uart_hangup, so we can</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* guarantee that info-&gt;tty will always contain something reasonable.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state = uart_get(drv, line);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (IS_ERR(state)) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; retval = PTR_ERR(state);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto fail;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Once we set tty-&gt;driver_data here, we are guaranteed that</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* uart_close() will decrement the driver module use count.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Any failures from here onwards should not touch the count.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; tty-&gt;driver_data = state;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; tty-&gt;low_latency = (state-&gt;port-&gt;flags &amp; UPF_LOW_LATENCY) ? 1 : 0;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; tty-&gt;alt_speed = 0;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;info-&gt;tty = tty;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* If the port is in the middle of closing, bail out now.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (tty_hung_up_p(filp)) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; retval = -EAGAIN;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;count--;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; mutex_unlock(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto fail;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Make sure the device is in D0 state.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (state-&gt;count == 1)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uart_change_pm(state, 0);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Start up the serial port.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; retval = uart_startup(state, 0);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* If we succeeded, wait until the port is ready.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (retval == 0)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; retval = uart_block_til_ready(filp, state);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_unlock(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* If this is the first open to succeed, adjust things to suit.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (retval == 0 &amp;&amp; !(state-&gt;info-&gt;flags &amp; UIF_NORMAL_ACTIVE)) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;info-&gt;flags |= UIF_NORMAL_ACTIVE;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uart_update_termios(state);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;fail:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return retval;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在这里函数里,继续完成操作的设备文件所对应state初始化.现在用户空间open这个设备了.即要对这个文件进行操作了.那uart_port也要开始工作了.即调用uart_startup()使其进入工作状态.当然,也需要初始化uart_port所对应的环形缓冲区circ_buf.即state-&gt;info-&gt; xmit.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">特别要注意,在这里将tty-&gt;driver_data = state;这是因为以后的操作只有port相关了,不需要去了解uart_driver的相关信息.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">跟踪看一下里面调用的两个重要的子函数. uart_get()和uart_startup().先分析uart_get().代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static struct uart_state *uart_get(struct uart_driver *drv, int line)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int ret = 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state = drv-&gt;state + line;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (mutex_lock_interruptible(&amp;state-&gt;mutex)) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ret = -ERESTARTSYS;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto err;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;count++;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!state-&gt;port || state-&gt;port-&gt;flags &amp; UPF_DEAD) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ret = -ENXIO;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto err_unlock;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!state-&gt;info) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;info = kzalloc(sizeof(struct uart_info), GFP_KERNEL);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (state-&gt;info) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; init_waitqueue_head(&amp;state-&gt;info-&gt;open_wait);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; init_waitqueue_head(&amp;state-&gt;info-&gt;delta_msr_wait);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Link the info into the other structures.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;port-&gt;info = state-&gt;info;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tasklet_init(&amp;state-&gt;info-&gt;tlet, uart_tasklet_action,</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp; (unsigned long)state);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; } else { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ret = -ENOMEM;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; goto err_unlock;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return state;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;err_unlock:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; state-&gt;count--;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; mutex_unlock(&amp;state-&gt;mutex);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;err:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return ERR_PTR(ret);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">从代码中可以看出.这里注要是操作是初始化state-&gt;info.注意port-&gt;info就是state-&gt;info的一个副本.即port直接通过port-&gt;info可以找到它要操作的缓存区.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">uart_startup()代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static int uart_startup(struct uart_state *state, int init_hw)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_info *info = state-&gt;info;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_port *port = state-&gt;port;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; unsigned long page;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int retval = 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (info-&gt;flags &amp; UIF_INITIALIZED)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Set the TTY IO error marker - we will only clear this</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* once we have successfully opened the port.&nbsp; Also set</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* up the tty-&gt;alt_speed kludge</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; set_bit(TTY_IO_ERROR, &amp;info-&gt;tty-&gt;flags);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (port-&gt;type == PORT_UNKNOWN)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Initialise and allocate the transmit and temporary</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* buffer.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!info-&gt;xmit.buf) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; page = get_zeroed_page(GFP_KERNEL);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (!page)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return -ENOMEM;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; info-&gt;xmit.buf = (unsigned char *) page;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uart_circ_clear(&amp;info-&gt;xmit);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; retval = port-&gt;ops-&gt;startup(port);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (retval == 0) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (init_hw) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Initialise the hardware port settings.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uart_change_speed(state, NULL);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* Setup the RTS and DTR signals once the</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* port is open and ready to respond.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (info-&gt;tty-&gt;termios-&gt;c_cflag &amp; CBAUD)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (info-&gt;flags &amp; UIF_CTS_FLOW) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; spin_lock_irq(&amp;port-&gt;lock);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (!(port-&gt;ops-&gt;get_mctrl(port) &amp; TIOCM_CTS))</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; info-&gt;tty-&gt;hw_stopped = 1;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; spin_unlock_irq(&amp;port-&gt;lock);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; info-&gt;flags |= UIF_INITIALIZED;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; clear_bit(TTY_IO_ERROR, &amp;info-&gt;tty-&gt;flags);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (retval &amp;&amp; capable(CAP_SYS_ADMIN))</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; retval = 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return retval;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">在这里,注要完成对环形缓冲,即info-&gt;xmit的初始化.然后调用port-&gt;ops-&gt;startup( )将这个port带入到工作状态.其它的是一个可调参数的设置,就不详细讲解了.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">七:设备节点的write操作</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">Write操作对应的操作接口为uart_write( ).代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static int</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">uart_write(struct tty_struct *tty, const unsigned char *buf, int count)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state = tty-&gt;driver_data;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_port *port;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct circ_buf *circ;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; unsigned long flags;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; int c, ret = 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; /*</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* This means you called this function _after_ the port was</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;* closed.&nbsp; No cookie for you.</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;*/</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!state || !state-&gt;info) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; WARN_ON(1);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return -EL3HLT;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; port = state-&gt;port;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; circ = &amp;state-&gt;info-&gt;xmit;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!circ-&gt;buf)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return 0;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; spin_lock_irqsave(&amp;port-&gt;lock, flags);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; while (1) { </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; c = CIRC_SPACE_TO_END(circ-&gt;head, circ-&gt;tail, UART_XMIT_SIZE);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (count &lt; c)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; c = count;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (c &lt;= 0)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; break;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; memcpy(circ-&gt;buf + circ-&gt;head, buf, c);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; circ-&gt;head = (circ-&gt;head + c) &amp; (UART_XMIT_SIZE - 1);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; buf += c;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; count -= c;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ret += c;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; }</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; spin_unlock_irqrestore(&amp;port-&gt;lock, flags);</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; uart_start(tty);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; return ret;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">Uart_start()代码如下:</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static void uart_start(struct tty_struct *tty)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state = tty-&gt;driver_data;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_port *port = state-&gt;port;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; unsigned long flags;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; spin_lock_irqsave(&amp;port-&gt;lock, flags);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; __uart_start(tty);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; spin_unlock_irqrestore(&amp;port-&gt;lock, flags);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">static void __uart_start(struct tty_struct *tty)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">{ </span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_state *state = tty-&gt;driver_data;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; struct uart_port *port = state-&gt;port;</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; if (!uart_circ_empty(&amp;state-&gt;info-&gt;xmit) &amp;&amp; state-&gt;info-&gt;xmit.buf &amp;&amp;</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; !tty-&gt;stopped &amp;&amp; !tty-&gt;hw_stopped)</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; port-&gt;ops-&gt;start_tx(port);</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">}</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">显然,对于write操作而言,它就是将数据copy到环形缓存区.然后调用port-&gt;ops-&gt;start_tx()将数据写到硬件寄存器.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">八:Read操作</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">Uart的read操作同Tty的read操作相同,即都是调用ldsic-&gt;read()读取read_buf中的内容.有对这部份内容不太清楚的,参阅&lt;&lt; linux设备模型之tty驱动架构&gt;&gt;.</span> 
          </div> 
          <div style="text-align: left;">
            &nbsp; 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">九:小结</span> 
          </div> 
          <div style="text-align: left;"> 
           <span style="font-size: small;">本小节是分析serial驱动的基础.在理解了tty驱动架构之后,再来理解uart驱动架构应该不是很难.随着我们在linux设备驱动分析的深入,越来越深刻的体会到,linux的设备驱动架构很多都是相通的.只要深刻理解了一种驱动架构.举一反三.也就很容易分析出其它架构的驱动了.</span> 
          </div> 
         </div> 
        </div> </td> 
      </tr> 
     </tbody> 
    </table> <p style="line-height: 150%; margin: 5px;">&nbsp;</p> </td> 
  </tr> 
  <tr> 
   <td> <p>&nbsp;<span style="color: #000099;"><strong>原文地址</strong></span> <a href="http://ericxiao.cublog.cn/" rel="nofollow">:http://ericxiao.cublog.cn/</a> </p> <p>&nbsp;</p> <p>&nbsp;</p> </td> 
  </tr> 
 </tbody> 
</table>

**linux终端设备uart应用程序实例**

<table style="width: 95%; border-collapse: collapse;"> 
 <tbody> 
  <tr> 
   <td> <p style="text-align: left; line-height: 150%; margin: 5px;"><code><span style="color: #000000;"><span style="color: #ff9900;">/***************** serial send ***************/</span><br><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>stdio<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*标准输入输出定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>stdlib<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*标准函数库定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>unistd<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*Unix标准函数定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>sys<span style="color: #0000cc;">/</span>types<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/**/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>sys<span style="color: #0000cc;">/</span>stat<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/**/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>fcntl<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*文件控制定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span>termios<span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*PPSIX终端控制定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">include</span> <span style="color: #0000cc;">&lt;</span><span style="color: #ff0000;">errno</span><span style="color: #0000cc;">.</span>h<span style="color: #0000cc;">&gt;</span> <span style="color: #ff9900;">/*错误号定义*/</span><br><span style="color: #0000cc;">#</span><span style="color: #ff0000;">define</span> <span style="color: #0000ff;">FALSE</span> <span style="color: #0000cc;">-</span>1<br><span style="color: #ff9900;">/*[url=]**@brief[/url] 设置串口通信速率<br>[email=*@param]*@param[/email] fd 类型 int 打开串口的文件句柄<br>[email=*@param]*@param[/email] speed 类型 int 串口速度<br>[email=*@return]*@return[/email] void*/</span><br><span style="color: #0000ff;">int</span> speed_arr<span style="color: #0000cc;">[</span><span style="color: #0000cc;">]</span> <span style="color: #0000cc;">=</span> <span style="color: #0000cc;">{ </span>B115200<span style="color: #0000cc;">,</span>B38400<span style="color: #0000cc;">,</span> B19200<span style="color: #0000cc;">,</span> B9600<span style="color: #0000cc;">,</span> B4800<span style="color: #0000cc;">,</span> B2400<span style="color: #0000cc;">,</span> B1200<span style="color: #0000cc;">,</span> B300<span style="color: #0000cc;">,</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;B38400<span style="color: #0000cc;">,</span> B19200<span style="color: #0000cc;">,</span> B9600<span style="color: #0000cc;">,</span> B4800<span style="color: #0000cc;">,</span> B2400<span style="color: #0000cc;">,</span> B1200<span style="color: #0000cc;">,</span> B300<span style="color: #0000cc;">,</span> <span style="color: #0000cc;">}</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">int</span> name_arr<span style="color: #0000cc;">[</span><span style="color: #0000cc;">]</span> <span style="color: #0000cc;">=</span> <span style="color: #0000cc;">{ </span>115200<span style="color: #0000cc;">,</span>38400<span style="color: #0000cc;">,</span> 19200<span style="color: #0000cc;">,</span> 9600<span style="color: #0000cc;">,</span> 4800<span style="color: #0000cc;">,</span> 2400<span style="color: #0000cc;">,</span> 1200<span style="color: #0000cc;">,</span> 300<span style="color: #0000cc;">,</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;38400<span style="color: #0000cc;">,</span> 19200<span style="color: #0000cc;">,</span> 9600<span style="color: #0000cc;">,</span> 4800<span style="color: #0000cc;">,</span> 2400<span style="color: #0000cc;">,</span> 1200<span style="color: #0000cc;">,</span> 300<span style="color: #0000cc;">,</span> <span style="color: #0000cc;">}</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">int</span> set_speed<span style="color: #0000cc;">(</span><span style="color: #0000ff;">int</span> fd<span style="color: #0000cc;">,</span> <span style="color: #0000ff;">int</span> speed<span style="color: #0000cc;">)</span><br><span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;<span style="color: #0000ff;">int</span> i<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">int</span> status<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">struct</span> termios Opt<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;tcgetattr<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span> <span style="color: #0000cc;">&amp;</span>Opt<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">for</span> <span style="color: #0000cc;">(</span> i<span style="color: #0000cc;">=</span> 0<span style="color: #0000cc;">;</span> i <span style="color: #0000cc;">&lt;</span> <span style="color: #0000ff;">sizeof</span><span style="color: #0000cc;">(</span>speed_arr<span style="color: #0000cc;">)</span> <span style="color: #0000cc;">/</span> <span style="color: #0000ff;">sizeof</span><span style="color: #0000cc;">(</span><span style="color: #0000ff;">int</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span> i<span style="color: #0000cc;">+</span><span style="color: #0000cc;">+</span><span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>speed <span style="color: #0000cc;">=</span><span style="color: #0000cc;">=</span> name_arr<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;tcflush<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span> TCIOFLUSH<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;cfsetispeed<span style="color: #0000cc;">(</span><span style="color: #0000cc;">&amp;</span>Opt<span style="color: #0000cc;">,</span> speed_arr<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;cfsetospeed<span style="color: #0000cc;">(</span><span style="color: #0000cc;">&amp;</span>Opt<span style="color: #0000cc;">,</span> speed_arr<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;status <span style="color: #0000cc;">=</span> tcsetattr<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span> TCSANOW<span style="color: #0000cc;">,</span> <span style="color: #0000cc;">&amp;</span>Opt<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>status <span style="color: #0000cc;">!</span><span style="color: #0000cc;">=</span> 0<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">perror</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"tcsetattr fd1"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;&nbsp;tcflush<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>TCIOFLUSH<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br><span style="color: #0000cc;">}</span><br><span style="color: #ff9900;">/**<br>[email=*@brief]*@brief[/email] 设置串口数据位，停止位和效验位<br>[email=*@param]*@param[/email] fd 类型 int 打开的串口文件句柄*<br>[email=*@param]*@param[/email] databits 类型 int 数据位 取值 为 7 或者8*<br>[email=*@param]*@param[/email] stopbits 类型 int 停止位 取值为 1 或者2*<br>[email=*@param]*@param[/email] parity 类型 int 效验类型 取值为N,E,O,,S<br>*/</span><br><span style="color: #0000ff;">int</span> set_Parity<span style="color: #0000cc;">(</span><span style="color: #0000ff;">int</span> fd<span style="color: #0000cc;">,</span><span style="color: #0000ff;">int</span> databits<span style="color: #0000cc;">,</span><span style="color: #0000ff;">int</span> stopbits<span style="color: #0000cc;">,</span><span style="color: #0000ff;">int</span> parity<span style="color: #0000cc;">)</span><br><span style="color: #0000cc;">{ </span><br><span style="color: #0000ff;">struct</span> termios options<span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span> tcgetattr<span style="color: #0000cc;">(</span> fd<span style="color: #0000cc;">,</span><span style="color: #0000cc;">&amp;</span>options<span style="color: #0000cc;">)</span> <span style="color: #0000cc;">!</span><span style="color: #0000cc;">=</span> 0<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">perror</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"SetupSerial 1"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">return</span><span style="color: #0000cc;">(</span><span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>CSIZE<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">switch</span> <span style="color: #0000cc;">(</span>databits<span style="color: #0000cc;">)</span> <span style="color: #ff9900;">/*设置数据位数*/</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">case</span> 7<span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> CS7<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">case</span> 8<span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> CS8<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">default</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;<span style="color: #ff0000;">fprintf</span><span style="color: #0000cc;">(</span><span style="color: #ff0000;">stderr</span><span style="color: #0000cc;">,</span><span style="color: #ff00ff;">"Unsupported data size/n"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">return</span><span style="color: #0000cc;">(</span><span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">switch</span> <span style="color: #0000cc;">(</span>parity<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'n'</span><span style="color: #0000cc;">:</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'N'</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>PARENB<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Clear parity enable */</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_iflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>INPCK<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Enable parity checking */</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'o'</span><span style="color: #0000cc;">:</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'O'</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">(</span>PARODD <span style="color: #0000cc;">|</span> PARENB<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* 设置为奇效验*/</span> <br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_iflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> INPCK<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Disnable parity checking */</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'e'</span><span style="color: #0000cc;">:</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'E'</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> PARENB<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Enable parity */</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>PARODD<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* 转换为偶效验*/</span> <br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_iflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> INPCK<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Disnable parity checking */</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'S'</span><span style="color: #0000cc;">:</span><br><span style="color: #0000ff;">case</span> <span style="color: #ff00ff;">'s'</span><span style="color: #0000cc;">:</span> <span style="color: #ff9900;">/*as no parity*/</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>PARENB<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>CSTOPB<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">default</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;<span style="color: #ff0000;">fprintf</span><span style="color: #0000cc;">(</span><span style="color: #ff0000;">stderr</span><span style="color: #0000cc;">,</span><span style="color: #ff00ff;">"Unsupported parity/n"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000cc;">(</span><span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #ff9900;">/* 设置停止位*/</span> <br>&nbsp;&nbsp;<span style="color: #0000ff;">switch</span> <span style="color: #0000cc;">(</span>stopbits<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">case</span> 1<span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">&amp;</span><span style="color: #0000cc;">=</span> <span style="color: #0000cc;">~</span>CSTOPB<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">case</span> 2<span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> CSTOPB<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">break</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">default</span><span style="color: #0000cc;">:</span><br>&nbsp;&nbsp;<span style="color: #ff0000;">fprintf</span><span style="color: #0000cc;">(</span><span style="color: #ff0000;">stderr</span><span style="color: #0000cc;">,</span><span style="color: #ff00ff;">"Unsupported stop bits/n"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000cc;">(</span><span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #ff9900;">/* Set input parity option */</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>parity <span style="color: #0000cc;">!</span><span style="color: #0000cc;">=</span> <span style="color: #ff00ff;">'n'</span><span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_iflag <span style="color: #0000cc;">|</span><span style="color: #0000cc;">=</span> INPCK<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cc<span style="color: #0000cc;">[</span>VTIME<span style="color: #0000cc;">]</span> <span style="color: #0000cc;">=</span> 150<span style="color: #0000cc;">;</span> <span style="color: #ff9900;">// 15 seconds<br></span><br>&nbsp;&nbsp;&nbsp;&nbsp;options<span style="color: #0000cc;">.</span>c_cc<span style="color: #0000cc;">[</span>VMIN<span style="color: #0000cc;">]</span> <span style="color: #0000cc;">=</span> 0<span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;tcflush<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>TCIFLUSH<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span> <span style="color: #ff9900;">/* Update the options and do it NOW */</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>tcsetattr<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>TCSANOW<span style="color: #0000cc;">,</span><span style="color: #0000cc;">&amp;</span>options<span style="color: #0000cc;">)</span> <span style="color: #0000cc;">!</span><span style="color: #0000cc;">=</span> 0<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">perror</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"SetupSerial 3"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000cc;">(</span><span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000cc;">(</span>0<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br><span style="color: #ff9900;">/**<br>[email=*@breif]*@breif[/email] 打开串口<br>*/</span><br><span style="color: #0000ff;">int</span> OpenDev<span style="color: #0000cc;">(</span><span style="color: #0000ff;">char</span> <span style="color: #0000cc;">*</span>Dev<span style="color: #0000cc;">)</span><br><span style="color: #0000cc;">{ </span><br><span style="color: #0000ff;">int</span> fd <span style="color: #0000cc;">=</span> <span style="color: #ff0000;">open</span><span style="color: #0000cc;">(</span>Dev<span style="color: #0000cc;">,</span> O_RDWR <span style="color: #0000cc;">|</span> O_NOCTTY <span style="color: #0000cc;">|</span> O_NDELAY<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span> <span style="color: #ff9900;">//| O_NOCTTY | O_NDELAY<br></span><br><span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span><span style="color: #0000cc;">-</span>1 <span style="color: #0000cc;">=</span><span style="color: #0000cc;">=</span> fd<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">{ </span> <span style="color: #ff9900;">/*设置数据位数*/</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">perror</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"Can't Open Serial Port"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">return</span> <span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br><span style="color: #0000ff;">else</span><br><span style="color: #0000ff;">return</span> fd<span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br><span style="color: #ff9900;">/**<br>[email=*@breif]*@breif[/email] main()<br>*/</span><br><span style="color: #0000ff;">int</span> main<span style="color: #0000cc;">(</span><span style="color: #0000ff;">int</span> argc<span style="color: #0000cc;">,</span> <span style="color: #0000ff;">char</span> <span style="color: #0000cc;">*</span><span style="color: #0000cc;">*</span>argv<span style="color: #0000cc;">)</span><br><span style="color: #0000cc;">{ </span><br><span style="color: #0000ff;">int</span> fd<span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">int</span> nwrite<span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">char</span> <span style="color: #0000cc;">*</span>buff<span style="color: #0000cc;">=</span><span style="color: #ff00ff;">"I am sending data!"</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">char</span> <span style="color: #0000cc;">*</span>dev <span style="color: #0000cc;">=</span><span style="color: #ff00ff;">"/dev/s3c2410_serial0"</span><span style="color: #0000cc;">;</span> <span style="color: #ff9900;">//扬创YC2440-S板子的串口名字</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>fd <span style="color: #0000cc;">=</span> OpenDev<span style="color: #0000cc;">(</span>dev<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">&gt;</span>0<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;&nbsp;set_speed<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>115200<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000ff;">else</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;<span style="color: #ff0000;">printf</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"Can't Open Serial Port!/n"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #ff0000;">exit</span><span style="color: #0000cc;">(</span>0<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">if</span> <span style="color: #0000cc;">(</span>set_Parity<span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>8<span style="color: #0000cc;">,</span>1<span style="color: #0000cc;">,</span><span style="color: #ff00ff;">'N'</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">=</span><span style="color: #0000cc;">=</span> <span style="color: #0000ff;">FALSE</span><span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">printf</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"Set Parity Error/n"</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">exit</span><span style="color: #0000cc;">(</span>1<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;<span style="color: #0000ff;">while</span><span style="color: #0000cc;">(</span>1<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000ff;">while</span><span style="color: #0000cc;">(</span><span style="color: #0000cc;">(</span>nwrite <span style="color: #0000cc;">=</span> <span style="color: #ff0000;">write</span><span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">,</span>buff<span style="color: #0000cc;">,</span><span style="color: #0000ff;">sizeof</span><span style="color: #0000cc;">(</span>buff<span style="color: #0000cc;">)</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">)</span><span style="color: #0000cc;">&gt;</span>0<span style="color: #0000cc;">)</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">{ </span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff9900;">/*sizeof(buff)=4 buff是指向字符串常量的字符指针*/</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">printf</span><span style="color: #0000cc;">(</span><span style="color: #ff00ff;">"/nLen %d/n"</span><span style="color: #0000cc;">,</span>nwrite<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff9900;">//buff[nread+1]='/0';<br></span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff9900;">//printf("/n%s",buff);<br></span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;&nbsp;<span style="color: #0000cc;">}</span><br>&nbsp;&nbsp;&nbsp;&nbsp;<span style="color: #ff0000;">close</span><span style="color: #0000cc;">(</span>fd<span style="color: #0000cc;">)</span><span style="color: #0000cc;">;</span><br><span style="color: #0000cc;">}</span><br><br><br></span></code></p> </td> 
  </tr> 
 </tbody> 
</table>

以上为在YC2440开发板上验证的uart应用开发程序，该程序包括设置波特率，停止位，校验位，字长等，直接在linux下编译，可以通过挂载根文件系统的方式调试，也可以直接拷贝到开发板的flash里直接运行。

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