Question

我正在尝试使用此处提供的示例开发LIN总线主控器：

https://github.com/trainman419/linux-lin/tree/master/misc/tty_lin_master

本质上，它通过串行端口发送LIN协议消息。

我稍微更改了代码，以便更简单地进行低级功能测试。我想看看LIN分析器是否能正确解码非常原始的LIN消息，但我遇到了与串口有关的奇怪问题。我在/ dev / ttymxc4（RS-232）接口上发送了几个连续的字符，但是我在数据包传输的中间位置看到了一个随机的暂停。有趣的是，这个暂停从某个值开始，我捕获了8.6毫秒但随后逐渐缩小，直到它消失了......但随后又重新开始。

基本上，如果你看一下main，我实际上只是通过RS-232发送10个字符......

以下是代码，如果有人有任何想法：

/*
 * UART-LIN master implementation
 */

 #define USE_TERMIOS2

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdint.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <time.h> /* clock_nanosleep */
#include <getopt.h>

#ifndef USE_TERMIOS2
  #include <linux/serial.h> /* struct struct_serial */
  #include <termios.h>
#else /*USE_TERMIOS2*/
  #include <asm/ioctls.h>
  #include <asm/termbits.h>
#endif /*USE_TERMIOS2*/

#include "lin_common.h"

#define LIN_HDR_SIZE        2

struct sllin_tty {
    int tty_fd;

#ifndef USE_TERMIOS2
    struct termios tattr_orig;
    struct termios tattr;
    struct serial_struct sattr;
#else /*USE_TERMIOS2*/
    struct termios2 tattr_orig;
    struct termios2 tattr;
#endif /*USE_TERMIOS2*/
};

struct sllin_tty sllin_tty_data;

struct sllin sllin_data = {
    .tty = &sllin_tty_data,
};

/* ------------------------------------------------------------------------ */

#ifndef USE_TERMIOS2

static int tty_set_baudrate(struct sllin_tty *tty, int baudrate)
{
    /* Set "non-standard" baudrate in serial_struct struct */
    tty->sattr.flags &= (~ASYNC_SPD_MASK);
    tty->sattr.flags |= (ASYNC_SPD_CUST);
    tty->sattr.custom_divisor = (tty->sattr.baud_base + baudrate / 2) / baudrate;
    if (ioctl(tty->tty_fd, TIOCSSERIAL, &tty->sattr) < 0)
    {
        perror("ioctl TIOCSSERIAL");
        return -1;
    }

    return 0;
}

static int tty_flush(struct sllin_tty *tty, int queue_selector)
{
    return tcflush(tty->tty_fd, queue_selector);
}

#else /*USE_TERMIOS2*/

static int tty_set_baudrate(struct sllin_tty *tty, int baudrate)
{
    tty->tattr.c_ospeed = baudrate;
    tty->tattr.c_ispeed = baudrate;
    tty->tattr.c_cflag &= ~CBAUD;
    tty->tattr.c_cflag |= BOTHER;

    if(ioctl(tty->tty_fd, TCSETS2, &tty->tattr)) {
        perror("ioctl TIOCSSERIAL");
        return -1;
    }

    return 0;
}

static int tty_flush(struct sllin_tty *tty, int queue_selector)
{
    return ioctl(tty->tty_fd, TCFLSH, queue_selector);
}

#endif /*USE_TERMIOS2*/


static int tty_set_mode(struct sllin_tty *tty, int baudrate)
{
    if(!isatty(tty->tty_fd)) {
        fprintf(stderr, "Not a terminal.\n");
        return -1;
    }

    /* Flush input and output queues. */
    if (tty_flush(tty, TCIOFLUSH) != 0) {
        perror("tcflush");
        return -1;;
    }

#ifndef USE_TERMIOS2

    /* Save settings for later restoring */
    if (tcgetattr(tty->tty_fd, &tty->tattr_orig) < 0) {
        perror("tcgetattr");
        return -1;
    }

    /* Save settings into global variables for later use */
    if (tcgetattr(tty->tty_fd, &tty->tattr) < 0) {
        perror("tcgetattr");
        return -1;
    }

    /* Save settings into global variables for later use */
    if (ioctl(tty->tty_fd, TIOCGSERIAL, &tty->sattr) < 0) {
        perror("ioctl TIOCGSERIAL");
    }

#else /*USE_TERMIOS2*/

    /* Save settings for later restoring */
    if (ioctl(tty->tty_fd, TCGETS2, &tty->tattr_orig) < 0) {
        perror("ioctl TCGETS2");
        return -1;
    }

    /* Save settings into global variables for later use */
    if (ioctl(tty->tty_fd, TCGETS2, &tty->tattr) < 0) {
        perror("ioctl TCGETS2");
        return -1;
    }

#endif /*USE_TERMIOS2*/

    /* 8 data bits                  */
    /* Enable receiver              */
    /* Ignore CD (local connection) */
    tty->tattr.c_cflag = CS8 | CREAD | CLOCAL;
    tty->tattr.c_iflag = 0;
    tty->tattr.c_oflag = NL0 | CR0 | TAB0 | BS0 | VT0 | FF0;
    tty->tattr.c_lflag = 0;

    tty->tattr.c_cc[VINTR]    = '\0';
    tty->tattr.c_cc[VQUIT]    = '\0';
    tty->tattr.c_cc[VERASE]   = '\0';
    tty->tattr.c_cc[VKILL]    = '\0';
    tty->tattr.c_cc[VEOF]     = '\0';
    tty->tattr.c_cc[VTIME]    = '\0';
    tty->tattr.c_cc[VMIN]     = 1;
    tty->tattr.c_cc[VSWTC]    = '\0';
    tty->tattr.c_cc[VSTART]   = '\0';
    tty->tattr.c_cc[VSTOP]    = '\0';
    tty->tattr.c_cc[VSUSP]    = '\0';
    tty->tattr.c_cc[VEOL]     = '\0';
    tty->tattr.c_cc[VREPRINT] = '\0';
    tty->tattr.c_cc[VDISCARD] = '\0';
    tty->tattr.c_cc[VWERASE]  = '\0';
    tty->tattr.c_cc[VLNEXT]   = '\0';
    tty->tattr.c_cc[VEOL2]    = '\0';

#ifndef USE_TERMIOS2
    /* Set TX, RX speed to 38400 -- this value allows
       to use custom speed in struct struct_serial */
    cfsetispeed(&tty->tattr, B38400);
    cfsetospeed(&tty->tattr, B38400);

    if (tcsetattr(tty->tty_fd, TCSANOW, &tty->tattr) == -1) {
        perror("tcsetattr()");
        return -1;
    }

#else /*USE_TERMIOS2*/

    /* Set new parameters with previous speed and left */
    /* tty_set_baudrate() to do the rest  */
    if(ioctl(tty->tty_fd, TCSETS2, &tty->tattr)) {
        perror("ioctl TIOCSSERIAL");
        return -1;
    }

#endif /*USE_TERMIOS2*/

    /* Set real speed */
    tty_set_baudrate(tty, baudrate);

    return 0;
}

int sllin_open(struct sllin *sl, const char *dev_fname, int baudrate)
{
    int fd;

    sl->lin_baud = baudrate;

    /* Calculate baudrate for sending LIN break */
    sl->lin_break_baud = (sl->lin_baud * 2) / 3;

    fd = open(dev_fname, O_RDWR);
    if (fd < 0) {
        perror("open()");
        return -1;
    }
    sl->tty->tty_fd = fd;

    return tty_set_mode(sl->tty, sl->lin_baud);
}

int main()
{
    struct sllin *sl = &sllin_data;

    char *dev_fname = "/dev/ttymxc4";
    int lin_baudrate = 19200;
    int lin_id = 1;

    if (sllin_open(sl, dev_fname, lin_baudrate) < 0) {
        fprintf (stderr, "sllin_open open failed\n");
        exit(EXIT_FAILURE);
    }

    fcntl(fileno(stdin), F_SETFL, O_NONBLOCK);
    printf("Press enter to terminate.\n\n");


    while(1) {
        char c;

        tty_flush(sl->tty, TCIOFLUSH);

        unsigned int buff[10] = {1,2,3,4,5,6,7,8,9,10};
        // debug
        write(sl->tty->tty_fd, &buff[0], 1);
        write(sl->tty->tty_fd, &buff[1], 1);
        write(sl->tty->tty_fd, &buff[2], 1);
        write(sl->tty->tty_fd, &buff[3], 1);
        write(sl->tty->tty_fd, &buff[4], 1);
        write(sl->tty->tty_fd, &buff[5], 1);
        write(sl->tty->tty_fd, &buff[6], 1);
        write(sl->tty->tty_fd, &buff[7], 1);
        write(sl->tty->tty_fd, &buff[8], 1);
        write(sl->tty->tty_fd, &buff[9], 1);
        // debug

        sleep(1);

        if (read(fileno(stdin), &c, 1) > 0)
            break;
    }

    return EXIT_SUCCESS;
}

Answer 1

基本上，如果你看看主要内容，我只是通过RS-232发送10个字符...

问题是你的输出方法而不是十个 write（）系统调用，每个只有一个字节（这是非常低效的），只使用一个 write（）作为十个字节的缓冲区。

假设这是在Linux下执行的，每个系统调用都会允许调度程序暂停您的进程（因此存在间隙）。
如果您只使用一个系统调用，那么设备驱动程序将尽可能快地传输数据（只有DMA或中断延迟可能导致xmit间隙）。

替换所有这些

    write(sl->tty->tty_fd, &buff[0], 1);
    write(sl->tty->tty_fd, &buff[1], 1);
    write(sl->tty->tty_fd, &buff[2], 1);
    write(sl->tty->tty_fd, &buff[3], 1);
    write(sl->tty->tty_fd, &buff[4], 1);
    write(sl->tty->tty_fd, &buff[5], 1);
    write(sl->tty->tty_fd, &buff[6], 1);
    write(sl->tty->tty_fd, &buff[7], 1);
    write(sl->tty->tty_fd, &buff[8], 1);
    write(sl->tty->tty_fd, &buff[9], 1);

只有这个

    write(sl->tty->tty_fd, buff, 10);

此外，使用 tcdrain（）替换写入和读取之间的 sleep（）。

连续UART传输之间的随机暂停

1 个答案: