Timers

This sample starts a timer that repeats five times by starting itself again from its callback, which wakes main() with a semaphore when done. It then starts one, reads how long it has left, and stops it.

The callback runs in the tick interrupt, so it only counts and signals. Work that has to block belongs in delayed work, which runs on a thread.

Run:: pbl samples samples/kernel/timer
Boards:: every board

Sources

src/main.c

#include <inttypes.h>

#include <pbl/kernel/delay.h>
#include <pbl/kernel/sem.h>
#include <pbl/kernel/time.h>
#include <pbl/kernel/timer.h>
#include <pbl/logging/logging.h>
#include <pbl/util/misc.h>

#define BLINKS          5
#define BLINK_PERIOD_MS 20

/* A timer lives in the object it acts on, which its callback gets back. */
struct blinker {
  struct pbl_timer timer;
  struct pbl_sem done;
  unsigned int blinks;
  uint64_t last_ms;
};

/* Callbacks run in the tick interrupt: keep them short, and never block. */
static void prv_blink(struct pbl_timer *timer) {
  struct blinker *blinker = container_of(timer, struct blinker, timer);

  blinker->blinks++;
  blinker->last_ms = pbl_uptime_ms();

  /* Timers are one-shot: one that repeats starts itself again. */
  if (blinker->blinks < BLINKS) {
    pbl_timer_start(timer, PBL_MSEC(BLINK_PERIOD_MS));
  } else {
    pbl_sem_give(&blinker->done);
  }
}

static struct blinker s_blinker = {
  .timer = PBL_TIMER_INITIALIZER(prv_blink),
  .done = PBL_SEM_INITIALIZER(0, 1),
};

int main(void) {
  uint64_t start_ms = pbl_uptime_ms();
  int ret;

  pbl_timer_start(&s_blinker.timer, PBL_MSEC(BLINK_PERIOD_MS));

  ret = pbl_sem_take(&s_blinker.done, PBL_SEC(1));
  if (ret != 0) {
    PBL_LOG_ERR("main: timer did not expire (%d)", ret);
    return ret;
  }

  PBL_LOG_INFO("main: %u blinks, the last one %s %u ms after the start", s_blinker.blinks,
               s_blinker.last_ms - start_ms >= BLINKS * BLINK_PERIOD_MS ? "at least" : "less than",
               BLINKS * BLINK_PERIOD_MS);

  s_blinker.blinks = 0;
  pbl_timer_start(&s_blinker.timer, PBL_SEC(10));
  pbl_sleep_ms(10);
  PBL_LOG_INFO("main: started for 10 s, active: %s, more than 5 s left: %s",
               pbl_timer_is_active(&s_blinker.timer) ? "yes" : "no",
               pbl_ticks_to_ms(pbl_timer_remaining(&s_blinker.timer)) > 5000 ? "yes" : "no");

  pbl_timer_stop(&s_blinker.timer);
  PBL_LOG_INFO("main: stopped, active: %s", pbl_timer_is_active(&s_blinker.timer) ? "yes" : "no");
  pbl_sleep_ms(20);
  PBL_LOG_INFO("main: stopped before it expired, %u blinks since", s_blinker.blinks);

  PBL_LOG_INFO("Sample done");

  return 0;
}

Output

main: 5 blinks, the last one at least 100 ms after the start
main: started for 10 s, active: yes, more than 5 s left: yes
main: stopped, active: no
main: stopped before it expired, 0 blinks since
Sample done

PebbleOS

Timers

Sources

Output

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