This project implements a long-duration digital watchdog timer with I2C interface. It runs on the inexpensive ATTINY412-SSN. It can be added to a custom PCB to provide a flexible watchdog functionality for a system.
Compile with Arduino IDE. Tested with Arduino 1.8.13. Install using a UPDI programmer.
Prerequisite libraries:
The device has a 7-bit I2C slave address of 0x32. There are three internal registers:
0x00 VERSION Read-only. 4 MSBs major version, 4 LSBs minor version.
0x01 CONFIG Enable the outputs (alert, reset, powercycle).
0x02 WDT Refresh and set the next timeout period.
The 8-bit timer decrements every timer tick. The first time it reaches zero the ALERT output is triggered (if enabled). The second time it reachs zero the RESET and/or POWERCYCLE outputs are triggered (if enabled). The timer tick period is 250 milliseconds (#define WDT_TICK_INTERVAL_MSEC), resulting in a maximum timeout of 64 seconds.
The Linux driver provides a standard /dev/watchdog interface. Build and install the driver:
cd driver
make
make install
Any userspace watchdog daemon can be used to control/refresh the watchdog, such as the Debian watchdog utility. Refer to the daemon docs for installation and configuration instructions.
The driver logs a message every time the watchdog is refreshed. On a system using /dev/watchdog2 at I2C address 0x32:
[578491.970519] attiny_wdt 2-0032: watchdog2: staring timer