[alsa-devel] pointer callback question

[Tim Blechmann]

hello takashi,

>>>> the brief log is (4 periods of 64 frames):
>>>> stream_pointer at 64
>>>> stream_pointer at 128
>>>> stream_pointer at 192
>>>> stream_pointer at 256
>>> This is invalid.  The pointer callback must return 0 in this case.
>>> The value the pointer callback returns is between 0 and buffer_size-1.
>> sry, typo, 5 periods of 64 frames
> 
> Then it must be OK.  If the stream is stopped, it's likely by the
> buffer underrun detection or so...
> 
> BTW, you should be sure that the buffer size is aligned to the period 
> size if such a design is assumed.  Without the extra constraint, it
> could be unaligned as default.

now i am trying to debug it some more. the lx6464es card provides
commands to send audio buffers to the card, and issues an interrupt,
when the buffer has been processed. i am using one dma buffer of
period_bytes*periods (128 frames, 3 bytes per sample, 64 channels, 5
periods)

for the startup, i am sending a number of buffers to the card (periods):
[ 2825.545296] LX6464ES: starting: buffer index 0 on ef620000 (24576 bytes)
[ 2825.545385] LX6464ES: starting: buffer index 1 on ef626000 (24576 bytes)
[ 2825.545474] LX6464ES: starting: buffer index 2 on ef62c000 (24576 bytes)
[ 2825.545568] LX6464ES: starting: buffer index 3 on ef632000 (24576 bytes)
[ 2825.545662] LX6464ES: starting: buffer index 4 on ef638000 (24576 bytes)

for each buffer, the card issues an `end of buffer' interrupt, in which
i send a new buffer to the card and call snd_pcm_period_elapsed with an
updated hw pointer:
[ 2825.548340] LX6464ES: interrupt: gave buffer index 0 on ef620000
(24576 bytes)
[ 2825.548385] LX6464ES: stream_pointer at 128
[ 2825.550986] LX6464ES: interrupt: gave buffer index 1 on ef626000
(24576 bytes)
[ 2825.551029] LX6464ES: stream_pointer at 256
[ 2825.553653] LX6464ES: interrupt: gave buffer index 2 on ef62c000
(24576 bytes)
[ 2825.553695] LX6464ES: stream_pointer at 384
[ 2825.556353] LX6464ES: interrupt: gave buffer index 3 on ef632000
(24576 bytes)
[ 2825.556397] LX6464ES: stream_pointer at 512
[ 2825.559014] LX6464ES: interrupt: gave buffer index 4 on ef638000
(24576 bytes)
[ 2825.559061] LX6464ES: stream_pointer at 0

directly after returning 0 from the pointer callback, alsa requests a stop:
[ 2825.559067] ->lx_pcm_trigger
the timing seems to be fine (2.7 ms for 128 frames).

any idea, why alsa wants to stop the transfer? am i missing something,
like to i need to inform alsa, that the cyclic buffer wraps around?

the code is available at [1]

thanks, tim

[1]
http://tim.klingt.org/git?p=digigram.git;a=shortlog;h=refs/heads/digigram

-- 
tim at klingt.org
http://tim.klingt.org

Relying on the government to protect your privacy is like asking a
peeping tom to install your window blinds.
  John Perry Barlow

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