ztimer: add ztimer_stopwatch convenience functions

[benpicco]

Contribution description

Ztimer is often used to measure time, but often without the needed ztimer_aquire().

Add some convenience functions that automatically do the right thing and that are easier to use than manually doing the time measuring code, so they will hopefully see more adoption over the error-prone open-coded solution.

Testing procedure

The benchmark function has been converted to use the new API. tests/bench_runtime_coreapis still works as before.

Issues/PRs references

[kfessel]

i like how this interface is flexible enough to be written like

typedef struct {
    ztimer_clock_t *clock;  /**< the clock to use     */
    ztimer zt;              /** some timer to keep this working */
    uint32_t start_time;    /**< start of measurement */
} ztimer_stopwatch_t;

static void _keep_active_cb(void *timer_ptr){
    if(!timer_ptr) return;
    ztimer_stopwatch_t timer = timer_ptr;
    ztimer_set(timer->clock, &timer->zt, 0xfff);
}

static inline void ztimer_stopwatch_init(ztimer_clock_t *clock, ztimer_stopwatch_t *timer)
{
    timer->clock = clock;
    timer->zt = { .callback=_keep_active_cb, .arg=timer };
}

static inline void ztimer_stopwatch_start(ztimer_stopwatch_t *timer)
{
    timer->zt.arg=timer;
    ztimer_set(timer->clock, &timer->zt, 0xfff);
    timer->start_time = ztimer_now(timer->clock);
}

static inline void ztimer_stopwatch_start_timout(ztimer_stopwatch_t *timer, uint32_t timeout)
{
    timer->zt.arg = (void *) 0;
    ztimer_set(timer->clock, &timer->zt, timeout);
    timer->start_time = ztimer_now(timer->clock);
}

static inline uint32_t ztimer_stopwatch_stop(ztimer_stopwatch_t *timer)
{
    uint32_t now = ztimer_now(timer->clock);
    ztimer_remove(timer->clock, &timer->zt)
    return now - timer->start_time;
}

[benpicco]

Now I'm confused - isn't the purpose of ztimer_ondemand that you don't need to keep a dummy timer running? Or did I misunderstand the purpose of that module?

[kfessel]

You are right this is the purpose of ondemand and this PR is good.
I am just thinking that acquire an release will lead to timer leakage or double release. And like how this interface can work without them. Missing something this was also a huge argument for acquire and release. We can even extend its functionality without acquire and release like counting more than 32Bit without requiring ztimer64, just by adding a small rollover-counter.

[riot-ci]

Murdock results

✔️ PASSED

d91c0e8 sys/benchmark: make use of ztimer stopwatch

Success	Failures	Total	Runtime
6919	0	6919	12m:40s

Artifacts

• Documentation preview

[kfessel]

nice API; implementation working great; test provided 👍

[benpicco]

bors merge

[bors]

Build succeeded:

• Murdock
• static-tests
• tools-build-success