Linux 驱动像单片机一样读取一帧dmx512串口数据
硬件全志R528
目标：实现Linux 读取一帧dmx512串口数据。
问题分析：因为串口数据量太大，帧与帧之间的间隔太小。通过Linux自带的读取函数方法无法获取到
帧头和帧尾，读取到的数据都是缓存区中的，数据量又大。导致缓冲区中一直有很多数据，
又由于dmx512数据协议中并没有帧头帧尾字段只有普通数据，无法通过特定的帧头帧尾截取到一完整帧的数据。
所以只能像单片机一样通过串口寄存器对LSR 的UART_LSR_FE位 （接收到错误帧）认为是一帧结束和开始。
通过对Linux驱动读取串口数据的过程分析，
tty_read() ----> ld->ops->read() ----> n_tty_read()
n_tty_read()中add_wait_queue(&tty->read_wait, &wait)没有数据的时候上层的read进程阻塞在此
而在串口有数据来的时候n_tty_receive_buf()--->wake_up_interruptible(&tty->read_wait)，唤醒上面的read进程n_tty_read()中会继续运行，将数据拷到用户空间
从整个分析来看，uart驱动会把从硬件接受到的数据暂时存放在tty_buffer里面，然后调用线路规程的receive_buf()把数据存放到tty->read_buf里面，
而系统调用的read()函数直接从tty->read_buf里面读取数据。
所以最终判断在uart的串口中断接收处理函数中增加接收代码比较合适。
Linux 设置非标准波特率参考上次的博客。
方法：
1、写一个简单字符驱动dmx512_uart.c，放在sunxi-uart.c同文件夹中。
在驱动读函数中设置全局变量标识，等待读取数据，后copy_to_user上传到用户空间.
修改同目录下的Makefile 和Kconfig 后添加到内核，编译到内核中。
Makefile 增加
obj-$(CONFIG_SERIAL_DMX512) += dmx512_uart.o ###+++++
Kconfig 增加选项
config SERIAL_DMX512
tristate "dmx512 uart driver"
default n
help
dmx512 uart driver
实际使用过程中发现驱动中等待读取数据时的msleep()函数，在R528系统中会影响阻塞其他线程的正常运行。
所以后来将msleep()更改为了等待队列
/*dmx512_uart.c 代码*/ #include <linux/module.h> #include <linux/slab.h> #include <linux/delay.h> #include <linux/fs.h> #include <linux/uaccess.h> #include <linux/init.h> #include <linux/cdev.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include "dmx512_uart.h" #define CDEV_NAME "dmx512_uart_dev" struct dmx512_uart_dev *dmx512_devp; static ssize_t dmx512drv_read (struct file *filp, char __user *buf, size_t size, loff_t *ppos) { int len =0; int num =0; int ret =0; int i=0; //printk("%s start\n",__func__); if(size > DMX512_BUF_LEN) { dmx512_devp->r_size = DMX512_BUF_LEN; } else { dmx512_devp->r_size = size; } memset(dmx512_devp->dmx_buff,0,sizeof(dmx512_devp->dmx_buff)); dmx512_devp->end_read_flag = false; dmx512_devp->recv_len =0; dmx512_devp->num_break =0; dmx512_devp->start_read_flag = true; #if 0 while(!dmx512_devp->end_read_flag) /*等待获取数据*/ { msleep(100); num++; if(num > 50) { printk("timeout\n"); break; } }
#endif
ret = wait_event_interruptible_timeout(dmx512_devp->rwq, dmx512_devp->end_read_flag == true, msecs_to_jiffies(5000));
if(!ret)
{
return -ETIMEDOUT;
}
if(dmx512_devp->recv_len < size) { len = dmx512_devp->recv_len; } else { len = size; } if(copy_to_user(buf,dmx512_devp->dmx_buff, len)) ret = -EFAULT; else{ ret = len; } //printk("%s end\n",__func__); return ret; } static ssize_t dmx512drv_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos) { return 0; } static int dmx512drv_close (struct inode *inodp, struct file *filp) { //printk("%s\n",__func__); return 0; } static int dmx512drv_open (struct inode *inodp, struct file *filp) { //printk("%s\n",__func__); return 0; } static const struct file_operations dmx512drv_fops = { .owner = THIS_MODULE, .open =dmx512drv_open, .read =dmx512drv_read, .write =dmx512drv_write, .release =dmx512drv_close, }; static int __init dmx512_init(void) { int ret; dmx512_devp =kzalloc(sizeof(struct dmx512_uart_dev), GFP_KERNEL); if(!dmx512_devp) { ret = -ENOMEM; return ret; } #if 0 /*动态申请dev*/ ret = alloc_chrdev_region(&dmx512_devp->dev,0, 1, CDEV_NAME); if(ret) { printk("failed to allocate char device region\n"); return ret; } cdev_init(&dmx512_devp->cdev,&dmx512drv_fops); ret = cdev_add(&dmx512_devp->cdev,dmx512_devp->dev,1); if(ret) { printk("failed to cdev_add\n"); goto unregister_chrdev; } return 0; unregister_chrdev: unregister_chrdev_region(dmx512_devp->dev,1); return ret; #endif dmx512_devp->dev_major = register_chrdev(0,"dmx512_uart_drv",&dmx512drv_fops); if(dmx512_devp->dev_major < 0) { printk(KERN_ERR"register_chrdev error\n"); ret =- ENODEV; goto err_0; } dmx512_devp->cls = class_create(THIS_MODULE,"dmx512_cls"); if(IS_ERR(dmx512_devp->cls)) { printk(KERN_ERR"class_create error\n"); ret = PTR_ERR(dmx512_devp->cls); goto err_1; } dmx512_devp->dev = device_create(dmx512_devp->cls, NULL,MKDEV(dmx512_devp->dev_major, 0),NULL,"dmx512_uart"); if(IS_ERR(dmx512_devp->dev)) { printk(KERN_ERR"device_create error\n"); ret = PTR_ERR(dmx512_devp->dev); goto err_2; }
init_waitqueue_head(&dmx512_devp->rwq); return 0; err_2: class_destroy(dmx512_devp->cls); err_1: unregister_chrdev(dmx512_devp->dev_major,"dmx512_uart_drv"); err_0: kfree(dmx512_devp); return ret; } static void __exit dmx512_exit(void) { #if 0 cdev_del(&dmx512_devp->cdev); unregister_chrdev_region(dmx512_devp->dev,1); #endif device_destroy(dmx512_devp->cls, MKDEV(dmx512_devp->dev_major, 0)); class_destroy(dmx512_devp->cls); unregister_chrdev(dmx512_devp->dev_major,"dmx512_uart_drv"); kfree(dmx512_devp); } module_init(dmx512_init); module_exit(dmx512_exit); MODULE_LICENSE("GPL"); /*dmx512_uart.h 头文件*/ #ifndef _DMX512_UART_H_ #define _DMX512_UART_H_ #define DMX512_BUF_LEN (4096+1+3) struct dmx512_uart_dev { unsigned int dev_major; struct class *cls; struct device *dev; int recv_len; int r_size; bool start_read_flag; bool end_read_flag; unsigned char num_break; unsigned char dmx_buff[DMX512_BUF_LEN];
wait_queue_head_t rwq; /*2023-3-20*/ }; extern struct dmx512_uart_dev *dmx512_devp; #endif /*_DMX512_UART_H_*/
2、串口接收中断处理函数中根据全局变量标识开始读取数据。
通过对寄存器LSR 的UART_LSR_FE位进行判断，为新的一帧的开始和结束。
通过对内核源码的分析找到uart的串口中断接收处理函数。在
sunxi-uart.c -》static unsigned int sw_uart_handle_rx(struct sw_uart_port *sw_uport, unsigned int lsr)
#include <linux/sched.h> //增加头文件
#include <linux/wait.h>
static unsigned int sw_uart_handle_rx(struct sw_uart_port *sw_uport, unsigned int lsr) { unsigned char ch = 0; int max_count = 256; char flag; #if IS_ENABLED(CONFIG_SERIAL_SUNXI_DMA) if ((sw_uport->dma->use_dma & RX_DMA)) { if (lsr & SUNXI_UART_LSR_RXFIFOE) { dev_info(sw_uport->port.dev, "error:lsr=0x%x\n", lsr); lsr = serial_in(&sw_uport->port, SUNXI_UART_LSR); return lsr; } } #endif if(lsr & SUNXI_UART_LSR_FE) { if((dmx512_devp->start_read_flag) && (strncmp(sw_uport->name,"uart1",5) ==0)) /*现在用的是uart1 不同的端口需要调整，也可以通过驱动直接传过来*/ { dmx512_devp->num_break++; if(dmx512_devp->num_break ==1) dmx512_devp->recv_len =0; } } do { if((dmx512_devp->start_read_flag) && (strncmp(sw_uport->name,"uart1",5) ==0)) { if((lsr & SUNXI_UART_LSR_FE) &&(max_count !=256)) dmx512_devp->num_break++; } if (likely(lsr & SUNXI_UART_LSR_DR)) { ch = serial_in(&sw_uport->port, SUNXI_UART_RBR); #if IS_ENABLED(CONFIG_SW_UART_DUMP_DATA) sw_uport->dump_buff[sw_uport->dump_len++] = ch; #endif } else ch = 0; flag = TTY_NORMAL; sw_uport->port.icount.rx++; if (unlikely(lsr & SUNXI_UART_LSR_BRK_ERROR_BITS)) { /* * For statistics only */ if (lsr & SUNXI_UART_LSR_BI) { lsr &= ~(SUNXI_UART_LSR_FE | SUNXI_UART_LSR_PE); sw_uport->port.icount.brk++; /* * We do the SysRQ and SAK checking * here because otherwise the break * may get masked by ignore_status_mask * or read_status_mask. */ if (!ch && uart_handle_break(&sw_uport->port)) goto ignore_char; } else if (lsr & SUNXI_UART_LSR_PE) sw_uport->port.icount.parity++; else if (lsr & SUNXI_UART_LSR_FE) sw_uport->port.icount.frame++; if (lsr & SUNXI_UART_LSR_OE) sw_uport->port.icount.overrun++; /* * Mask off conditions which should be ignored. */ lsr &= sw_uport->port.read_status_mask; #if IS_ENABLED(CONFIG_SERIAL_SUNXI_CONSOLE) if (sw_is_console_port(&sw_uport->port)) { /* Recover the break flag from console xmit */ lsr |= sw_uport->lsr_break_flag; } #endif if (lsr & SUNXI_UART_LSR_BI) flag = TTY_BREAK; else if (lsr & SUNXI_UART_LSR_PE) flag = TTY_PARITY; else if (lsr & SUNXI_UART_LSR_FE) flag = TTY_FRAME; } if (uart_handle_sysrq_char(&sw_uport->port, ch)) goto ignore_char; //printk("sw_uport->name =%s\n",sw_uport->name); /*增加对break的判断*/ if((dmx512_devp->start_read_flag) && (strncmp(sw_uport->name,"uart1",5) ==0)) { if(dmx512_devp->num_break ==1) { dmx512_devp->dmx_buff[dmx512_devp->recv_len] =ch; dmx512_devp->recv_len++; if(dmx512_devp->recv_len >= dmx512_devp->r_size) { dmx512_devp->start_read_flag = false; dmx512_devp->end_read_flag = true; wake_up_interruptible(&dmx512_devp->rwq); } } else if(dmx512_devp->num_break > 1) { dmx512_devp->start_read_flag = false; dmx512_devp->end_read_flag = true; wake_up_interruptible(&dmx512_devp->rwq); } } uart_insert_char(&sw_uport->port, lsr, SUNXI_UART_LSR_OE, ch, flag); ignore_char: lsr = serial_in(&sw_uport->port, SUNXI_UART_LSR); } while ((lsr & (SUNXI_UART_LSR_DR | SUNXI_UART_LSR_BI)) && (max_count-- > 0)); SERIAL_DUMP(sw_uport, "Rx"); spin_unlock(&sw_uport->port.lock); tty_flip_buffer_push(&sw_uport->port.state->port); spin_lock(&sw_uport->port.lock); return lsr; }
3、写应用程序进行验证。
打开设置串口uart1 波特率250000 8 N 2
#include<stdio.h> #include<stdlib.h> #include<string.h> #include <sys/time.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <termios.h> #include <errno.h> #include <signal.h> #include <stdbool.h> #define UART1_DEV_NAME "/dev/ttyS1" /*需根据实际端口修改*/ #define DMX512_DEV_NAME "/dev/dmx512_uart" #define BUF_LEN 100 #define MAX_BUF 2048 int oflags =0; int fd =-1; char buff[MAX_BUF] ={0}; /** *@brief 配置串口 *@param fd:串口文件描述符. nSpeed:波特率， nBits:数据位 7 or 8， nEvent:奇偶校验位， nStop：停止位 *@return 失败返回-1；成功返回0； */ int set_serial(int fd, int nSpeed, int nBits, char nEvent, int nStop) { struct termios newttys1, oldttys1; /*保存原有串口配置*/ if(tcgetattr(fd, &oldttys1) != 0) { perror("Setupserial 1"); return - 1; } memset(&newttys1, 0, sizeof(newttys1)); //memcpy(&newttys1, &oldttys1, sizeof(newttys1)); /*CREAD 开启串行数据接收,CLOCAL并打开本地连接模式*/ newttys1.c_cflag |= (CLOCAL | CREAD); newttys1.c_cflag &=~CSIZE; /*设置数据位*/ switch(nBits) /*数据位选择*/ { case 7: newttys1.c_cflag |= CS7; break; case 8: newttys1.c_cflag |= CS8; break; default:break; } switch(nEvent) /*奇偶校验位*/ { case '0': newttys1.c_cflag |= PARENB; /*开启奇偶校验*/ newttys1.c_iflag |= (INPCK | ISTRIP); /*INPCK打开输入奇偶校验，ISTRIP 去除字符的第八个比特*/ newttys1.c_cflag |= PARODD; /*启动奇校验（默认为偶校验）*/ break; case 'E': newttys1.c_cflag |= PARENB; /*开启奇偶校验*/ newttys1.c_iflag |= (INPCK | ISTRIP); /*INPCK打开输入奇偶校验，ISTRIP 去除字符的第八个比特*/ newttys1.c_cflag &= ~PARODD; /*启动偶校验*/ break; case 'N': newttys1.c_cflag &= ~PARENB; /*无奇偶校验*/ break; default:break; } switch(nSpeed) /*设置波特率*/ { case 2400: cfsetispeed(&newttys1, B2400); cfsetospeed(&newttys1, B2400); break; case 4800: cfsetispeed(&newttys1, B4800); cfsetospeed(&newttys1, B4800); break; case 9600: cfsetispeed(&newttys1, B9600); cfsetospeed(&newttys1, B9600); break; case 115200: cfsetispeed(&newttys1, B115200); cfsetospeed(&newttys1, B115200); break; case 250000: //ret = cfsetispeed(&newttys1, 0020001); //printf("reti = %d\n",ret); //ret = cfsetospeed(&newttys1, 0020001); //printf("reto = %d\n",ret); newttys1.c_cflag |= 0020001; break; default : cfsetispeed(&newttys1, B9600); cfsetospeed(&newttys1, B9600); break; } /*设置停止位*/ /*停止位为1，则清除CSTOPB,如停止位为2，则激活CSTOPB*/ if(nStop == 1) { newttys1.c_cflag &= ~CSTOPB; /*默认为停止位1*/ } else if(nStop == 2) { newttys1.c_cflag |= CSTOPB; } newttys1.c_iflag &=~(PARMRK); /*不设置的*/ newttys1.c_iflag |= IGNBRK ; /*设置的*/ printf("newttys1.c_iflag= 0x%\n",newttys1.c_iflag); /*设置最少字符和等待时间，对于接收字符和等待时间没有特别的要求时*/ newttys1.c_cc[VTIME] = 0; /*非规范模式读取时的超时时间*/ newttys1.c_cc[VMIN] = 0; /*非规范模式读取时的最小字符数*/ /*tcflush 清空终端未完成的输入、输出请求及数据 TCIFLUSH表示清空正接收到的数据，且不读取出来*/ tcflush(fd, TCIFLUSH); /*激活配置使其生效*/ if((tcsetattr(fd, TCSANOW, &newttys1)) != 0) { perror("usart set error"); return - 1; } return 0; } int main(int argc,char const * argv[]) { int ret =-1; int i =0; int n =0; int len = BUF_LEN; int baud = 250000; int fd_dmx512 =-1; struct sigaction saio; if(argc !=2) { printf("arg is not 2,arg is app baud_rate\n"); } if(argc == 2) baud = atoi(argv[1]); printf("baud =%d\n",baud); fd = open(UART1_DEV_NAME, O_RDWR | O_NOCTTY | O_NDELAY); if(fd < 0) { perror("Can't open uart1 port"); return(void *)"uart1 dev error"; } ret = set_serial(fd,baud, 8, 'N', 2); /*可能需要根据情况调整*/ if(ret < 0) { printf("set_serial error\n"); return -1; } while(1) { fd_dmx512 =open(DMX512_DEV_NAME,O_RDONLY); if(fd_dmx512 < 0) { printf("open dmx512 device error\n"); return -1; } memset(buff,0,sizeof(buff)); printf("Read start\n"); n = read(fd_dmx512,buff,600); printf("Read end\n"); printf("num=%d :",n); for(i=0;i<n;i++) printf("%02x ",buff[i]); printf("\n"); ret = close(fd_dmx512); if(ret < 0) printf("close error\n"); sleep(5); } return 0; }
通过测试后正常读取到串口数据
DMX512协议解析
（1）采用RS-485总线收发器，差分电压进行传输的，抗干扰能力强，信号可以进行长距离传输；
（2）不论调光数据是否需要改变，主机都必须发送控制信号。
（3）由于数据帧之间的时间小于1s，所以在1s内没有收到新的数据帧，说明信号已经丢失；
（4）因为是数据是调光用的，使用环境是不做安全要求的设备， 并且是不间断传输的，所以不需要复杂的校验。
dmx512协议串口波特率为250000
一个bit位 4us
8个位(Slot:x) 4*8=32us，x是从1到512
break 88us(范围是88μs——1ms)
MAB（Mark After Break） 8us 两个bit位的时间，高电平
start bit 4us 是低电平
Start Code（SC） 32us，8个位,是一段低电平，必须要有，串口表现中数据是0，接收时作头的一部分
stop 8us 两位结束，是高电平
MTBP 0-1s(MARK Time aftet slot，每一个数据间隔的空闲时间，是高电平，可以不要。
一帧数据包括 start + Slotx: + stop + MTBP = 4+32+8+0=44us
参考文档
