D12CWdt

1 Watchdog 编程

本章介绍YY3588看门狗的使用

1.1 命令行简单控制

# 查看节点
ls -l /dev/watchdog

# 写入任意内容（大写字母‘V’除外），开启看门狗 --- 每44秒内需要喂一次狗
echo A > /dev/watchdog

# 开启看门狗 --- 内核每21秒喂一次狗
echo V > /dev/watchdog

1.2 C 语言小 demo

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/types.h>
#include <linux/watchdog.h>

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <timeout>\n", argv[0]);
        return 1;
    }

    int timeout = atoi(argv[1]);

    printf("Timeout is set to %d seconds\n", timeout);
    int current_timeout;
    int num = 0;
    int fd = open("/dev/watchdog", O_RDWR);
    if (fd == -1) {
        perror("open /dev/watchdog");
        exit(EXIT_FAILURE);
    }

    if (ioctl(fd, WDIOC_SETTIMEOUT, &timeout) == -1) {
        perror("ioctl WDIOC_SETTIMEOUT");
        close(fd);
        exit(EXIT_FAILURE);
    }

    if (ioctl(fd, WDIOC_GETTIMEOUT, &current_timeout) == -1) {
        perror("ioctl WDIOC_GETTIMEOUT");
        close(fd);
        exit(EXIT_FAILURE);
    }
    printf("Current watchdog timeout is %d seconds\n", current_timeout);

    while (1) {
        if (ioctl(fd, WDIOC_KEEPALIVE, NULL) == -1) {
            perror("ioctl WDIOC_KEEPALIVE");
            close(fd);
            exit(EXIT_FAILURE);
        }
        printf("%d : feed the dog, Ctrl+c to exit.\n", ++num);
        sleep(10);
    }

    close(fd);
    printf("Watchdog device closed\n");

    return 0;
}

使用SDK中自带的交叉编译器SDK/prebuilts/gcc/linux-x86/aarch64/gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu/bin/aarch64-none-linux-gnu-gcc编译生成可执行文件，推送到板端运行。
效果如下：

$ ./a.out 5
Timeout is set to 5 seconds
Current watchdog timeout is 5 seconds
feed the dog
feed the dog

1.3 WDT精度说明

WDT精度只有16档，相邻档位计数相差⽐较⼤，因此⽆法精细计数。
关于设置的时长和实际的时间长度参考下表

命令行请求的超时时间	程序通过 ioctl 获取的超时时间	watchdog最终设置的超时时间
> 89	timeout_get = timeout_request	89
44 < timeout_request <= 89	89	89
22 < timeout_request <= 44	44	44
11 < timeout_request <= 22	22	22
5 < timeout_request <= 11	11	11
2 < timeout_request <= 5	5	5
timeout_request = 2	2	2
timeout_request = 1	1	1

1.4 暂停功能

# 暂停计数
io -4 0xfd58c000 0x00010001
# 恢复计数
io -4 0xfd58c000 0x00100000