[LAD] Fw: Re: Deriving a steady MIDI clock crossplatform?

----- Forwarded message from Fons Adriaensen <fons(a)linuxaudio.org> ----- Date: Thu, 19 May 2022 22:22:12 +0200 From: Fons Adriaensen <fons(a)linuxaudio.org> To: "Jeanette C." <julien(a)mail.upb.de> On Thu, May 19, 2022 at 07:52:33PM +0200, Jeanette C. wrote: The key to do this is to have a high priority thread waiting for an *absolute* time, and then each time increment that time by the required delta. Note that this is fundamentally different from using sleep or similar functions. With those you wait for a certain time. So if your previous event was late, the next one will be late as well just because you start waiting for it too late. So all the errors will add up, and you will *never* get the correct event frequency. When you wait until an absolute time, any latency on the previous event does not affect the following ones. The errors don't accumulate. So what to wait for ? That could be any system call that takes an absolute timeout rather than a maximum waiting time. On Linux I'd use something like sem_timedwait(). To set the initial timeout, the corresponding clock can be read with clock_gettime(), using the CLOCK_MONOTONIC option. Don't know about Apple. Last time I looked it didn't have clock_gettime(), but it has gettimeofday(). Note that it is not gettimeofday() that is the cause of the problem you mentioned, it is using sleep() or usleep(). Ciao, -- FA ----- End forwarded message -----