USB Watchdog for Linux

usbwdd.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <termios.h>
#include <fcntl.h>
#include <errno.h>

#define USBWD_SYN           ((unsigned char)0x80)
#define USBWD_ACK           ((unsigned char)0x81)
#define USBWD_PWRST         ((unsigned char)0xFF)

#define USBWD_MIN_TIMEOUT   ((unsigned char)0x01)
#define USBWD_MAX_TIMEOUT   ((unsigned char)0x7F)

#define USBWD_OK            ((unsigned char)0x82)
#define USBWD_FAIL          ((unsigned char)0x83)


void close_usbwd(int fd)
{
    close(fd);
}

int open_usbwd(const char* path)
{
    struct termios newtio;
    int fd = open(path, O_RDWR | O_NOCTTY);
    
    if (fd == -1)
        return -1;
    
    memset(&newtio, 0x00, sizeof(newtio));
    
    newtio.c_cflag |= B9600;
    newtio.c_cflag |= CS8;
    newtio.c_cflag |= CLOCAL;
    newtio.c_cflag |= CREAD;
    newtio.c_iflag = IGNPAR;
    newtio.c_oflag = 0;
    newtio.c_cc[VTIME] = 0;
    newtio.c_cc[VMIN] = 1;
    newtio.c_cc[VEOF] = 4;
    
    if (tcflush(fd, TCIFLUSH))
    {
        close_usbwd(fd);
        return -1; 
    }
    
    if (tcsetattr(fd, TCSANOW, &newtio))
    {
        close_usbwd(fd);
        return -1; 
    }
    
    return fd;
}

unsigned char sigout(int fd, unsigned char b)
{
    if (write(fd, &b, 1) == -1)
        return USBWD_FAIL;
    return USBWD_OK;
}

unsigned char sigin(int fd)
{
    unsigned char b = 0x00;
    if (read(fd, &b, 1) == -1)
        return USBWD_FAIL;
    return b;
}

int main(int argc, char** argv)
{
    if (argc != 2)
    {
        printf("usage: usbwd ttyfile\n");
        return 0;
    }

    int fd = open_usbwd(argv[1]);
    
    if (fd == -1)
    {
        printf("Cannot open USBWatchdog device\n");
        return -1;
    }
    
    // Send SYN signal, USBWatchdog is started
    if (sigout(fd, USBWD_SYN) != USBWD_OK)
        goto cleanup;
    
    // USBWatchdog send ACK signal to system
    if (sigin(fd) != USBWD_ACK)
        goto cleanup;
    
    // Send PWRST(0xFF) signal, reset system immediately
    // if (sigout(fd, USBWD_PWRST) == USBWD_OK)
    //
    // Timeout range: [USBWD_MIN_TIMEOUT, USBWD_MAX_TIMEOUT]
    // Timeout can be calcluated from "Timeout = 10 x T"
    while (sigout(fd, USBWD_MIN_TIMEOUT) == USBWD_OK)
        sleep(1);
    
    cleanup:
    close_usbwd(fd);
    return 0;
}