linux终端设备uart驱动分析

一:前言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.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.二:uart驱动架构概貌如下图所示:上图中红色部份标识即为uart部份的操作.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.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.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.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.三:uart驱动中重要的数据结构及其关联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: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:/dev/ttyS0 /dev/ttyS1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.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?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回忆tty驱动架构中.tty_driver有一个叫成员指向一个数组,即tty->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.那在uart驱动中,是否也可用相同的方式来处理呢?将uart驱动常用的数据结构表示如下:结合上面提出的疑问.可以很清楚的看懂这些结构的设计.四:uart_driver的注册操作Uart_driver注册对应的函数为: uart_register_driver()代码如下:int uart_register_driver(struct uart_driver *drv){ struct tty_driver *normal = NULL; int i, retval; BUG_ON(drv->state); /* * Maybe we should be using a slab cache for this, especially if * we have a large number of ports to handle. */ drv->state = kzalloc(sizeof(struct uart_state) * drv->nr, GFP_KERNEL); retval = -ENOMEM; if (!drv->state) goto out; normal = alloc_tty_driver(drv->nr); if (!normal) goto out; drv->tty_driver = normal; normal->owner = drv->owner; normal->driver_name = drv->driver_name; normal->name = drv->dev_name; normal->major = drv->major; normal->minor_start = drv->minor; normal->type = TTY_DRIVER_TYPE_SERIAL; normal->subtype = SERIAL_TYPE_NORMAL; normal->init_termios = tty_std_termios; normal->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL; normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 9600; normal->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV; normal->driver_state = drv; tty_set_operations(normal, &uart_ops); /* * Initialise the UART state(s). */ for (i = 0; i < drv->nr; i++) { struct uart_state *state = drv->state + i; state->close_delay = 500; /* .5 seconds */ state->closing_wait = 30000; /* 30 seconds */ mutex_init(&state->mutex); } retval = tty_register_driver(normal);out: if (retval < 0) { put_tty_driver(normal); kfree(drv->state); } return retval;}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->state的存储空间.这样,就会注册uart_driver->nr个设备节点.主设备号为uart_driver-> major. 开始的次设备号为uart_driver-> minor.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-> 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.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^_^).流程图如下:五: uart_add_one_port()操作在前面提到.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.顾名思义,这个函数是在uart_driver增加一个port.代码如下:int uart_add_one_port(struct uart_driver *drv, struct uart_port *port){ struct uart_state *state; int ret = 0; struct device *tty_dev; BUG_ON(in_interrupt()); if (port->line >= drv->nr) return -EINVAL; state = drv->state + port->line; mutex_lock(&port_mutex); mutex_lock(&state->mutex); if (state->port) { ret = -EINVAL; goto out; } state->port = port; state->pm_state = -1; port->cons = drv->cons; port->info = state->info; /* * If this port is a console, then the spinlock is already * initialised. */ if (!(uart_console(port) && (port->cons->flags & CON_ENABLED))) { spin_lock_init(&port->lock); lockdep_set_class(&port->lock, &port_lock_key); } uart_configure_port(drv, state, port); /* * Register the port whether it’s detected or not. This allows * setserial to be used to alter this ports parameters. */ tty_dev = tty_register_device(drv->tty_driver, port->line, port->dev); if (likely(!IS_ERR(tty_dev))) { device_can_wakeup(tty_dev) = 1; device_set_wakeup_enable(tty_dev, 0); } else printk(KERN_ERR "Cannot register tty device on line %d/n", port->line); /* * Ensure UPF_DEAD is not set. */ port->flags &= ~UPF_DEAD;out: mutex_unlock(&state->mutex); mutex_unlock(&port_mutex); return ret;}首先这个函数不能在中断环境中使用. Uart_port->line就是对uart设备文件序号.它对应的也就是uart_driver->state数组中的uart_port->line项.它主要初始化对应uart_driver->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.操作流程图如下所示:六:设备节点的open操作在用户空间执行open操作的时候,就会执行uart_ops->open. Uart_ops的定义如下:static const struct tty_operations uart_ops = { .open = uart_open, .close = uart_close, .write = uart_write, .put_char = uart_put_char, .flush_chars = uart_flush_chars, .write_room = uart_write_room, .chars_in_buffer= uart_chars_in_buffer, .flush_buffer = uart_flush_buffer, .ioctl = uart_ioctl, .throttle = uart_throttle, .unthrottle = uart_unthrottle, .send_xchar = uart_send_xchar, .set_termios = uart_set_termios, .stop = uart_stop, .start = uart_start, .hangup = uart_hangup, .break_ctl = uart_break_ctl, .wait_until_sent= uart_wait_until_sent,#ifdef CONFIG_PROC_FS .read_proc = uart_read_proc,#endif .tiocmget = uart_tiocmget, .tiocmset = uart_tiocmset,};对应open的操作接口为uart_open.代码如下:static int uart_open(struct tty_struct *tty, struct file *filp){ struct uart_driver *drv = (struct uart_driver *)tty->driver->driver_state; struct uart_state *state; int retval, line = tty->index; BUG_ON(!kernel_locked()); pr_debug("uart_open(%d) called/n", line); /* * tty->driver->num won’t change, so we won’t fail here with * tty->driver_data set to something non-NULL (and therefore * we won’t get caught by uart_close()). */ retval = -ENODEV; if (line >= tty->driver->num) goto fail; /* * We take the semaphore inside uart_get to guarantee that we won’t * be re-entered while allocating the info structure, or while we * request any IRQs that the driver may need. This also has the nice * side-effect that it delays the action of uart_hangup, so we can * guarantee that info->tty will always contain something reasonable. */ state = uart_get(drv, line); if (IS_ERR(state)) { retval = PTR_ERR(state); goto fail; } /* * Once we set tty->driver_data here, we are guaranteed that * uart_close() will decrement the driver module use count. * Any failures from here onwards should not touch the count. */ tty->driver_data = state; tty->low_latency = (state->port->flags & UPF_LOW_LATENCY) ? 1 : 0; tty->alt_speed = 0; state->info->tty = tty; /* * If the port is in the middle of closing, bail out now. */ if (tty_hung_up_p(filp)) { retval = -EAGAIN; state->count–; mutex_unlock(&state->mutex); goto fail; } /* * Make sure the device is in D0 state. */ if (state->count == 1) uart_change_pm(state, 0); /* * Start up the serial port. */ retval = uart_startup(state, 0); /* * If we succeeded, wait until the port is ready. */ if (retval == 0) retval = uart_block_til_ready(filp, state); mutex_unlock(&state->mutex); /* * If this is the first open to succeed, adjust things to suit. */ if (retval == 0 && !(state->info->flags & UIF_NORMAL_ACTIVE)) { state->info->flags |= UIF_NORMAL_ACTIVE; uart_update_termios(state); }fail: return retval;}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->info-> xmit.特别要注意,在这里将tty->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.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:static struct uart_state *uart_get(struct uart_driver *drv, int line){ struct uart_state *state; int ret = 0; state = drv->state + line; if (mutex_lock_interruptible(&state->mutex)) { ret = -ERESTARTSYS; goto err; } state->count++; if (!state->port || state->port->flags & UPF_DEAD) { ret = -ENXIO; goto err_unlock; } if (!state->info) { state->info = kzalloc(sizeof(struct uart_info), GFP_KERNEL); if (state->info) { init_waitqueue_head(&state->info->open_wait); init_waitqueue_head(&state->info->delta_msr_wait); /* * Link the info into the other structures. */ state->port->info = state->info; tasklet_init(&state->info->tlet, uart_tasklet_action, (unsigned long)state); } else { ret = -ENOMEM; goto err_unlock; } } return state;err_unlock: state->count–; mutex_unlock(&state->mutex);err: return ERR_PTR(ret);}从代码中可以看出.这里注要是操作是初始化state->info.注意port->info就是state->info的一个副本.即port直接通过port->info可以找到它要操作的缓存区.uart_startup()代码如下:static int uart_startup(struct uart_state *state, int init_hw){ struct uart_info *info = state->info; struct uart_port *port = state->port; unsigned long page; int retval = 0; if (info->flags & UIF_INITIALIZED) return 0; /* * Set the TTY IO error marker – we will only clear this * once we have successfully opened the port. Also set * up the tty->alt_speed kludge */ set_bit(TTY_IO_ERROR, &info->tty->flags); if (port->type == PORT_UNKNOWN) return 0; /* * Initialise and allocate the transmit and temporary * buffer. */ if (!info->xmit.buf) { page = get_zeroed_page(GFP_KERNEL); if (!page) return -ENOMEM; info->xmit.buf = (unsigned char *) page; uart_circ_clear(&info->xmit); } retval = port->ops->startup(port); if (retval == 0) { if (init_hw) { /* * Initialise the hardware port settings. */ uart_change_speed(state, NULL); /* * Setup the RTS and DTR signals once the * port is open and ready to respond. */ if (info->tty->termios->c_cflag & CBAUD) uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR); } if (info->flags & UIF_CTS_FLOW) { spin_lock_irq(&port->lock); if (!(port->ops->get_mctrl(port) & TIOCM_CTS)) info->tty->hw_stopped = 1; spin_unlock_irq(&port->lock); } info->flags |= UIF_INITIALIZED; clear_bit(TTY_IO_ERROR, &info->tty->flags); } if (retval && capable(CAP_SYS_ADMIN)) retval = 0; return retval;}在这里,注要完成对环形缓冲,即info->xmit的初始化.然后调用port->ops->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.七:设备节点的write操作Write操作对应的操作接口为uart_write( ).代码如下:static intuart_write(struct tty_struct *tty, const unsigned char *buf, int count){ struct uart_state *state = tty->driver_data; struct uart_port *port; struct circ_buf *circ; unsigned long flags; int c, ret = 0; /* * This means you called this function _after_ the port was * closed. No cookie for you. */ if (!state || !state->info) { WARN_ON(1); return -EL3HLT; } port = state->port; circ = &state->info->xmit; if (!circ->buf) return 0; spin_lock_irqsave(&port->lock, flags); while (1) { c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE); if (count < c) c = count; if (c <= 0) break; memcpy(circ->buf + circ->head, buf, c); circ->head = (circ->head + c) & (UART_XMIT_SIZE – 1); buf += c; count -= c; ret += c; } spin_unlock_irqrestore(&port->lock, flags); uart_start(tty); return ret;}Uart_start()代码如下:static void uart_start(struct tty_struct *tty){ struct uart_state *state = tty->driver_data; struct uart_port *port = state->port; unsigned long flags; spin_lock_irqsave(&port->lock, flags); __uart_start(tty); spin_unlock_irqrestore(&port->lock, flags);}static void __uart_start(struct tty_struct *tty){ struct uart_state *state = tty->driver_data; struct uart_port *port = state->port; if (!uart_circ_empty(&state->info->xmit) && state->info->xmit.buf && !tty->stopped && !tty->hw_stopped) port->ops->start_tx(port);}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->ops->start_tx()将数据写到硬件寄存器.八:Read操作Uart的read操作同Tty的read操作相同,即都是调用ldsic->read()读取read_buf中的内容.有对这部份内容不太清楚的,参阅<< linux设备模型之tty驱动架构>>.九:小结本小节是分析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.

原文地址 :http://ericxiao.cublog.cn/

linux终端设备uart应用程序实例

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

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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