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。

/*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 "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;

    while(!dmx512_devp->end_read_flag) /*等待获取数据*/
    {
        msleep(100);
        num++;
        if(num > 50)
        {
            printk("timeout\n");
            break;
        }
    }
    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;
    }
    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];
};

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)

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;

                }
            }
            else if(dmx512_devp->num_break > 1)
            {
                    dmx512_devp->start_read_flag = false;
                    dmx512_devp->end_read_flag = true;

            }
        }

        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

(19条消息) DMX512协议解析_春风得意吃火锅的博客-CSDN博客_dmx512协议标准

(19条消息) tty驱动 read 过程梳理_0x460的博客-CSDN博客