Introduction

Architecture

Watchdog driver follows Linux’s Watchdog core, Watchdog device system. Watchdog device system provides watchdog interfaces to user space. The watchdog software architecture is illustrated in the following figure.

../../_images/watchdog_software_arch.svg — Watchdog software architecture

Note

The hardware watchdog device for Linux system is watchdog 4.

For more details on Linux watchdog system, refer to https://www.kernel.org/doc/html/v5.4/watchdog/index.html.

Implementation

Watchdog driver is implemented as following files:

Driver location	Introduction
<linux>/drivers/rtkdrivers/watchdog/Kconfig	Watchdog driver Kconfig
<linux>/drivers/rtkdrivers/watchdog/Makefile	Watchdog driver Makefile
<linux>/drivers/rtkdrivers/watchdog/realtek-wdg.c	Watchdog functions.

Configuration

DTS Configuration

Watchdog DTS node:

watchdog: wdg@410004C0 {
   compatible = "realtek,ameba-watchdog";
   reg = <0x410004C0 0x000010>;
   interrupts = <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH>;
   rtk,wdg-index = <4>;
   rtk,wdg-timeout = <30>; // seconds
   rtk,wdg-max-timeout-ms = <0xFFFF>; // 1~0xFFFF
   rtk,wdg-window-protection-ms = <0xFFFF>; // 0xFFFF means disabled, usually: disabled.
   rtk,wdg-int-trigger-threshold-ms = <50>;
   rtk,wdg-interrupt-mode = <1>;
};

The DTS configurations of watchdog are listed below:

Property	Description	Configurable?
compatible	The description of Watchdog driver. Default: “realtek,ameba-watchdog”.	No
reg	The hardware address and size for Watchdog device. Default: <0x410004C0 0x000010>	No
interrupts	The GIC number of Watchdog device. Default: <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH>	No
rtk,wdg-index	Realtek watchdog index. Default: <4>, a non-secure watchdog timer for CA32	No
rtk,wdg-timeout	Watchdog timeout in seconds	1~65
rtk,wdg-max-timeout-ms	Max watchdog timeout in ms, limited by hardware	1~0xFFFF
rtk,wdg-window-protection-ms	0xFFFF means that watchdog window protection is disabled. If set n between 0 to 0xFFFE means: during watchdog window n, this watchdog cannot be refreshed. Usually, the window is disabled.	0~0xFFFF
rtk,wdg-interrupt-mode	Generate an interrupt for CPU, when watchdog has not been refreshed for wdg-timeout minus wdg-int-trigger-threshold-ms. Default: open interrupt mode.	0/1
rtk,wdg-int-trigger-threshold-ms	If interrupt mode enabled, this is a threshold for watchdog hardware interrupt CPU before watchdog timeout. Default: 50ms	0~0xFFFF

Build Configuration

Select Device Drivers > Drivers for Realtek > Watchdog driver:

../../_images/watchdog_driver.png — Watchdog driver

APIs

APIs for User Space

Watchdog interfaces for user space are provided by <linux>/drivers/watchdog/watchdog_dev.c. Here are some commonly used APIs:

Interface	Introduction
watchdog_open	Open an watchdog device
watchdog_write	Ping watchdog
watchdog_ioctl	Configure watchdog parameters. Can ping watchdog as well.

For more APIs, refer to https://www.kernel.org/doc/html/v5.4/watchdog/watchdog-api.html.

Watchdog demo for user space is located at <test>/watchdog. Read readme.txt in the directory for more details.

APIs for Kernel Space

None.