std/wdt — Watchdog timer

import std/wdt

The watchdog timer resets the microcontroller if the program fails to “kick” it within a configured timeout — a standard safety net against lockups. Enable it, then call @wdt_reset regularly in your main loop; if a hang stops the resets, the watchdog fires and restarts the device.

Timeout (prescaler) values

@wdt_enable takes the watchdog prescaler value, which selects the timeout. That is why the example passes 6 rather than 1000: 6 selects the ~1 second timeout. The values map roughly as follows on classic AVR (the exact times scale with the watchdog oscillator and vary slightly by device):

Value	Approx. timeout
0	16 ms
1	32 ms
2	64 ms
3	0.125 s
4	0.25 s
5	0.5 s
6	1 s
7	2 s
8	4 s
9	8 s

Values 8 and 9 (4 s / 8 s) require the wider prescaler field present on most modern AVR parts. Pick a timeout comfortably longer than your worst-case loop iteration so normal operation never trips it.

@wdt_enable($prescaler: u8)

Enable the watchdog with a timeout selected by $prescaler — see the table above for the value-to-timeout mapping.

@wdt_reset()

Reset (kick) the watchdog timer, restarting its countdown. Call this often enough that it is reached before the timeout elapses. Implemented around the AVR WDR instruction.

@wdt_disable()

Disable the watchdog timer.

Example

target atmega328p
import std/wdt

@main {
    @wdt_enable(6)                 # arm the watchdog, ~1 s timeout (device-dependent)
    loop * {
        @do_work()                 # your real work; must finish within the timeout
        @wdt_reset()               # "kick" the watchdog to prove we are alive
    }
}