Timers

PeriodicTimer: call a function at a fixed interval from the kernel's timer service, without a task of your own.

Purpose

Heartbeats, watchdog kicks, polling a status pin: short work on a fixed period. The callback runs in the kernel timer task, so it must be short and must not block.

Example

#include <cstdint>
#include "PeriodicTimer.h"

static void Heartbeat(uint32_t arg) {
    (void)arg;                                         // runs in the timer service task
}

static PeriodicTimer heartbeat;

bool StartHeartbeat() {
    return heartbeat.Create("Heartbeat", Heartbeat, /*arg=*/0, /*periodMs=*/500,
                            /*autoStart=*/true);
}

void PauseHeartbeat() { heartbeat.Stop(); }
void ResumeHeartbeat() { heartbeat.Start(); }

API

Member	Does	Returns
Create(name, callback, arg, periodMs, autoStart = false)	Creates the kernel timer; starts it when autoStart	False if already created or the kernel refused
Start() / Stop()	Activate or deactivate	True on success
Destroy()	Stops and deletes the kernel timer; safe when never created	True on success
IsValid()		True between a successful Create() and Destroy()

The callback signature is void (*)(uint32_t); arg is passed to it on every call. The destructor deletes the timer.

Memory and timing

• One kernel timer per object, created in Create(). The object itself holds a handle and a flag.
• The period is converted to ticks with os_convert_msec_to_delay_ticks(), ms * tick_rate / 1000, rounded down but never to zero: on a 100 Hz tick 25 ms becomes 2 ticks (20 ms), and anything from 1 to 19 ms becomes 1 tick (10 ms). Use whole ticks. The tick rate is configTICK_RATE_HZ on FreeRTOS.
• Callbacks share one task. A slow callback delays every other timer in the system; hand longer work to a BaseThread or a queue.

Next: Generic templates.