SDK • Pico2W repeating alarm fails after about 1000 alarms

I reduced this to a simple case from a larger project.

The pico-sdk is up-to-date with github. I build the code with either define BOARD as pico2_w or pico in CMakeLists.txt, depending on the whether I am using pico or pico2_w..

The code below fails after about 1000 alarm callbacks on a Pico2_w. It works for several hours on a Pico.
EDIT: on a later try, on a pico, the repeating alarm failed after 33050 callbacks. So the repeating alarm fails on both a pico and a pico2_w.

An earlier, similar bug was closed as complete.

What am I doing wrong?

/////////////////////////////////////////////////////////////////////////////
// includes
#include <stdio.h>
#include "pico/stdlib.h"

/////////////////////////////////////////////////////////////////////////////
// global variables
volatile int count;

/////////////////////////////////////////////////////////////////////////////
// repeating timer callback
bool repeating_timer_callback(struct repeating_timer *t) {
++count;
return true;
}

/////////////////////////////////////////////////////////////////////////////
// main
int main() {
stdio_init_all();

printf("\nTest repeating timer\n");

// Create a repeating timer
static struct repeating_timer timer;

#include <stdio.h>
#include "pico/stdlib.h"

/////////////////////////////////////////////////////////////////////////////
// global variables
volatile int count;

/////////////////////////////////////////////////////////////////////////////
// repeating timer callback
bool repeating_timer_callback(struct repeating_timer *t) {
++count;
return true;
}

/////////////////////////////////////////////////////////////////////////////
// blink the led


/////////////////////////////////////////////////////////////////////////////
// main
int main() {
stdio_init_all();

printf("\nTest repeating timer\n");

// Create a repeating timer
static struct repeating_timer timer;

// Negative delay so means we will call repeating_timer_callback,
// and call it again 500ms later regardless of how long the
// callback took to execute
add_repeating_timer_ms(-50, repeating_timer_callback, NULL, &timer);
//sleep_ms(1000); // allow time to setup usb tty and skip the first few expirations

while (1) {
if ((count > 0) && ((count %50) == 0)) {
printf("At time %ld, count %d\n", time_us_32(), count);
}
sleep_ms(100); // wait until at least 1 timer expirations

}

cancel_repeating_timer(&timer);

while (1); // do not run off the end ...

return 0;
}

add_repeating_timer_ms(-50, repeating_timer_callback, NULL, &timer);

while (1) {
if ((count > 0) && ((count %50) == 0)) {
printf("At time %ld, count %d\n", time_us_32(), count);
}
sleep_ms(100); // wait until at least 1 timer expirations

}

cancel_repeating_timer(&timer);

while (1); // do not run off the end ...

return 0;
}

Statistics: Posted by tomdean — Wed Jan 28, 2026 6:34 am

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