Timing auxiliary tasks

Ward

I'm trying to have a thread responsible for drawing an OLED gui to execute somewhat regularly. Currently I use usleep() to have it execute about every 20ms or so but as some menu's have more drawing and text function calls they might take a bit longer to draw.

I'm looking for a low overhead sleep until X function and I've been looking at the Xenomai documentation for this. Would int rt_task_sleep_until ( RTIME date ) be a suitable function together with RTTIME rt_timer_read ( void ) be a good approach?

giuliomoro

you can't use the rt_ API (now known as alchemy), you should use the POSIX API. As I mentioned in our call, you can use clock_nanosleep() with CLOCK_MONOTONIC and TIMER_ABSTIME. That will give you a pseudo-periodic task, but you'll need to get a timestamp (with clock_gettime()) when the animation starts, then you can compute the desired time of future frames based on that.

However, if one or more frames overrun the allocated period, then later calls to clock_nanosleep() may return immediately and you may experience a backlog and there doesn't seem to be an easy way of detecting that from the return values of clock_nanosleep(). If there is a chance of this happening, maybe you are better off calling clock_gettime() and compute a value for nanosleep() at every frame instead. This way you can detect "underruns" and react to them appropriately (e.g.: skipping the next frame unless it's the last one ).

giuliomoro

btw a canonical way of scheduling auxiliary task at specific intervals is to count samples from within render() and call Bela_scheduleAuxiliaryTask() from there when appropriate. If the task is not done running it will not be rescheduled, so depending on how you write your code this could be a way to both have the thread running at fixed intervals and to avoid piling up of frames the way it would when returning immediately from clock_gettime().