On Tue, 14 Feb 2023 at 16:32, Fons Adriaensen <f...@linuxaudio.org> wrote: > > On Tue, Feb 14, 2023 at 03:57:05PM +0100, Wim Taymans wrote: > > > > The real difference between the two methods is 'sample count' > > > versus 'time' as the source of the event that starts a period. > > > > > > I always wondered why one would use a timer, it just amounts > > > to polling. Suppose you look every 1 ms to check if there > > > > You don't need to use polling with timerfd, just set the timeout > > according to some clock, > > add the timerfd to some poll loop and it wakes up on time. > > It's of course not 'active polling' (spending all CPU time on > testing a condition), but it is still polling in the sense > that it is NOT the event you wait for (having enough samples > to start a Jack cycle) that wakes you up. When using a timer > you just test for that condition periodically, which means > you can be up to that period late.
The idea is to use a DLL to tweak the timeout and wake up exactly when you have the desired number of samples in the device. > > To avoid loss of period processing time, the timer period > must a very small fraction of the Jack period time. And > then I wonder what is the advantage. > If you want to implement dynamic latency changes with the IRQ based wakeup you need to do the opposite, use small ALSA periods and then accumulate a few until you have the desired period for the graph. It would be possible to implement something like this as an alternative for timers. > > Very much like how ALSA wakes you up when a period expires. > > AFAIK, ALSA doesn't use timers for that. > For a sound card on e.g. a PCI bus the start of cycle would > be the indirect result of an hardware interrupt. For USB > or firewire cards, it would be triggered by an event from > the lower (USB/firewire) layers. > > BTW, what about the 'signed differences' issue I pointed > out earlier ? Should be fixed with this: https://gitlab.freedesktop.org/pipewire/pipewire/-/commit/274b63e9723ec00dd413bb64b6650d2004f7e4c2 Wim > > Ciao, > > -- > FA > _______________________________________________ Linux-audio-dev mailing list -- linux-audio-dev@lists.linuxaudio.org To unsubscribe send an email to linux-audio-dev-le...@lists.linuxaudio.org
