API target [LWN.net]

API target

Posted Oct 20, 2009 9:32 UTC (Tue) by njs (subscriber, #40338)
In reply to: API target by pharm
Parent article: LPC: The past, present, and future of Linux audio

But, uh, the mmap functions can't possibly be supported over an emulated-in-userspace sound device, i.e., what we're all using now that our "alsa" output is going to pulseaudio?

A better API is clearly needed, but I don't think it involves mmap.

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API target

Posted Oct 20, 2009 10:57 UTC (Tue) by cladisch (✭ supporter ✭, #50193) [Link]

> But, uh, the mmap functions can't possibly be supported over an emulated-in-userspace sound device

Classic mmap() can't. However, the ALSA API requires that the applications tells when and where it wants to access the buffer, and when it is done, so it is possible to emulate mmap on top on devices without a memory buffer. (In that case, the extra buffer adds latency, of course.)

> A better API is clearly needed

ALSA has snd_pcm_forward/rewind functions to move around in the buffer. However, these functions are optional, and the PulseAudio plugin does not implement them.