Epoll读取错误的字节

Question

所有消息的尾部都有2个字节的crc。11 b5表示消息开始。消息长度应为36字节。72 b5是另一个消息开始标记。112字节长度。73 b5也是消息标记。36字节。请找到蓝色下划线：这是一条好消息。小红胖胖的红是不好的。它是37字节长度。我有一个额外的字节和crc不匹配。下一个好的（绿色）。下一个坏消息。它是114字节而不是112字节，当然crc不匹配。

这是我的代码：

... All necessary includes

#define SERIAL_BAUD 921600
#define MAXEVENTS 1024

int openSerial()
{
struct termios options;
int fd;

if ((fd = open("/dev/ttyUSB0", O_RDWR)) == -1)
{
    return -1;
}

if (tcgetattr(fd, &options) < 0)
{
    printf("Unable to get options with tcgetattr\n");
    return -1;
}

if (cfsetispeed(&options, SERIAL_BAUD) < 0)
{
    printf("Unable to set input speed with cfsetispeed\n");
    return -1;
}

if (cfsetospeed(&options, SERIAL_BAUD) < 0)
{
    printf("Unable to set output speed with cfsetispeed\n");
    return -1;
}

cfmakeraw(&options);

//options.c_cflag |= SERIAL_BAUD; // Set Baudrate first time
options.c_cflag |= (CLOCAL | CREAD);
options.c_cflag &= ~CRTSCTS;

options.c_cflag &= ~ECHO; // Disable echoing of input characters
options.c_cflag &= ~ECHOE;

 // set to 8N1
options.c_cflag &= ~PARENB; // no parity
options.c_cflag &= ~CSTOPB; // 1 stop bit
options.c_cflag &= ~CSIZE; // Mask the character size bits
options.c_cflag |= CS8; // 8 data bits

options.c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);

options.c_oflag = 0;

options.c_cc[VTIME] = 2; // inter-character timer
options.c_cc[VMIN] = 1; // blocking read until

if (tcflush(fd, TCIFLUSH) < 0)
{
    printf("Unable to flush fd with tcflush\n");
    return -1;
}

if (tcsetattr(fd, TCSANOW, &options) != 0)
{
    printf("Unable to set options with tcsetattr\n");
    return -1;
}

return fd;
}

int main(void)
{
int fd;
int efd;
struct epoll_event event;
struct epoll_event* events;
int length;
unsigned char buff[512];

if ((fd = openSerial()) < 0)
{
    printf("Exiting because of openSerial failure\n");
    return 1;
}

efd = epoll_create1(0);

event.data.fd = fd;
event.events = EPOLLIN;

if (epoll_ctl(efd, EPOLL_CTL_ADD, fd, &event) < 0)
{
    printf("Epoll_ctl error occured\n");
    return 1;
}

events = (epoll_event*) calloc(MAXEVENTS, sizeof(event));

for(;;)
{
    int n = epoll_wait(efd, events, MAXEVENTS, 5000);

    if (n < 0)
    {
        // No ready descriptors, so wait a bit longer
        continue;
    }

    if(events[0].events & EPOLLIN)
    {
        length = read(events[0].data.fd, buff, sizeof(buff) / 2);

        if(length > 0)
        {
            printf("\n------MESSAGE START-------\n");
            for (int i = 0 ; i < length ; ++i)
            {
                if (i && i % 16 == 0)
                {
                    printf("\n");
                }
                printf("%02x ", buff[i]);
            }

            printf("\n------MESSAGE FINISH-------\n");
        }
    }
    else if(events[0].events & EPOLLOUT)
    {
        // TODO Write here to serial
    }
    else if(events[0].events & EPOLLHUP || events[0].events & EPOLLERR)
    {
        printf("Error occured on serial port\n");
    }
    else
    {
        printf("No data whthin 5 seconds.\n");
    }
}

free(events);
close(fd);

return 0;
}

Answer 1

您的问题是，read（）返回的字节无法满足您的期望。我认为没有理由相信埃波尔与此有关。

我也看不出有任何理由认为，read（）传递的字节与从设备dev/ttyUSB0接收的字节不同。如果这些与您预期的不同，那么我倾向于认为要么是设备出现故障，要么是您的预期不正确（或者至少不完整）。