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Rockchip Developer Guide Linux WDT

:::info 文档信息

文档标识：RK-KF-YF-083　·　发布版本：V1.1.0　·　发布日期：2021-04-13　·　页数：8　·　语言：英文

原始文档：Rockchip_Developer_Guide_Linux_WDT_EN.pdf

:::

章节大纲​

  • Rockchip Developer Guide Linux WDT（P1）
    • WDT Driver（P6）
      • DTS Node Configuration（P6）
    • WDT Usage（P6）
    • Kernel Configuration（P7）
    • FAQ（P7）
      • WDT Can't Stop（P7）
      • WDT Accuracy（P7）
      • PAUSE COUNTING（P8）

在线预览​

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1. WDT Driver​

The driver file is in:

drivers/watchdog/dw_wdt.c

1.1 DTS Node Configuration​

The reference document for DTS configuration is Documentation/devicetree/bindings/watchdog/dw_wdt.txt ，this document mainly introduces the follow parameter :

interrupts = <GIC_SPI 120 IRQ_TYPE_LEVEL_HIGH 0>;

The interrupt mode is to trigger an interrupt first, and then generate a reset signal after a timeout period.

clocks = <&cru PCLK_WDT>;

This attribute function is to drive WDT to work, and calculate each counting cycle.

2. WDT Usage​

The application operates the /dev/watchdog node to control the watchdog. Examples are as follows:

int main(void)
{
int fd = open("/dev/watchdog", O_WRONLY);    //here through open to start
watchdog
int ret = 0;
if (fd == -1) {
perror("watchdog");
exit(EXIT_FAILURE);
}
while (1) {
ret = write(fd, "\0", 1);     //Feed dogs by write
if (ret != 1) {
ret = -1;
break;
}
sleep(10);
}
close(fd);
return ret;
}

About close()

  1. Under normal condition, executing close () , which no longer feeding the dog and watchdog restart automatically . echo A > /dev/watchdog , where any characters other than character V are written

  2. write (fd," V ", 1); Then close () , write uppercase V, the kernel continues to feed the dog, the system will not automatically restart.

echo V > /dev/watchdog
  1. Configure the macro CONFIG_WATCHDOG_NOWAYOUT , repeat step 2, the kernel will not continue to feed the dog, and the system will be restarted.

3. Kernel Configuration​

Symbol: WATCHDOG [=y]
Type  : boolean
Prompt: Watchdog Timer Support
Location:
(1) -> Device Drivers
Defined at drivers/watchdog/Kconfig:6

4. FAQ​

4.1 WDT Can't Stop​

The legacy version of WDT does not have a matched register to configure the stop function, which can only be stopped by disable clock or soft reset. The clock or reset operation of some Rockchip' s product can only be performed in a safe environment. The new version of WDT adds a stop function in the future.

4.2 WDT Accuracy​

The accuracy of WDT is only 16 levels, and the counting of adjacent level is quite different, so it cannot be counted finely.

0000: 0x0000ffff
0001: 0x0001ffff
0010: 0x0003ffff
0011: 0x0007ffff
0100: 0x000fffff
0101: 0x001fffff
0110: 0x003fffff
0111: 0x007fffff
1000: 0x00ffffff
1001: 0x01ffffff
1010: 0x03ffffff
1011: 0x07ffffff
1100: 0x0fffffff
1101: 0x1fffffff
1110: 0x3fffffff
1111: 0x7fffffff

Assuming that the wdt clock is 100MHz, the maximum timeout time is 0x7fffffff/100MHz = 21 seconds. If a larger timeout is required, the corresponding WDT clock needs to be adjusted.

4.3 PAUSE COUNTING​

RK356X add pause counting function, use io command that from Rockchip or busybox's devmem to test pause counting and resume counting.

enable

CONFIG_DEVMEM

disable

CONFIG_STRICT_DEVMEM

Address 0xfdc60504 belongs to the register GRF_SOC_CON1 of SYS_GRF. write 0x1 to bit4 pause counting, write 0x0 to bit4 resume counting. Higher 16 bits are writable mask bits.

pause counting.

io -4 0xfdc60504 0x00100010

or

busybox devmem 0xfdc60504 32 0x00100010

resume counting.

io -4 0xfdc60504 0x00100000

or

busybox devmem 0xfdc60504 32 0x00100000