[LAD] ALSA latency and MMAP

Paul Davis paul at linuxaudiosystems.com
Mon Sep 7 12:11:02 UTC 2009

On Mon, Sep 7, 2009 at 4:53 AM, Clemens Ladisch<clemens at ladisch.de> wrote:
> Paul Davis wrote:
>> if you use read/write, you deliver/receive the data to/from the kernel
>> at the time of calling. but there is then an extra buffer inside the
>> ALSA midlevel driver code that holds the data till it is needed (in
>> both directions).
> There is no extra buffer for these functions; snd_pcm_write/read* copy
> the data to/from the same hardware buffer that would be used by the mmap
> functions.

snd_pcm_write() and snd_pcm_read(), IIRC, allow reads&writes of chunks
of data that are not period-sized. am i misremembering?

do you have an alternate explanation for louis' timing observations? error?

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