[alsa-devel] snd_pcm_hw_params_set_buffer_time_near: invalid argument

[Raymond Yau]

2011/3/9 Jaroslav Kysela <perex at perex.cz>

> On Wed, 9 Mar 2011, Jean-Yves Avenard wrote:
>
>  Hi
>>
>> On Wednesday, 9 March 2011, Raymond Yau <superquad.vortex2 at gmail.com>
>> wrote:
>>
>>  hda-intel.c only allocate 64Kbytes
>>>
>>>     /* buffer pre-allocation */
>>>     snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,
>>>                           snd_dma_pci_data(chip->pci),
>>>                           1024 * 64, 32 * 1024 * 1024);
>>>
>>> user or distribution need to change "prealloc" from 64 to a higher value
>>> for
>>> getting 500ms buffer
>>>
>>> echo 1024 > /proc/asound/Intel/pcm0p/sub0/prealloc
>>>
>>
>> It seems you misunderstood my first message.
>>
>> For a start, the default memory allocated to alsa in ubuntu is 4096kB.
>> so the amount of ram isn't the problem.
>>
>> Setting a buffer of
>> 200ms: ok
>> 300ms: ok
>> 400ms: not ok (invalid argument)
>> 500ms: ok
>>
>> Why would 400ms gives invalid argument, when 500ms doesn't nor 300.
>> Memory available is obviously not the issue.
>>
>> If only 64kB is allocated, requesting 200ms gives you 200ms
>> 300ms -> 300ms
>> 400ms -> invalid argument
>> 500ms -> 371ms
>> 600ms -> 371ms
>>
>> You would assume that requesting 400ms would work or return what can
>> fit in what has been pre-allocated.
>>
>
> What is your dir argument (last one) for the near functions? If it's NULL
> or value is zero, it means you request the exact value which may not be
> available. Use -1 to request specified or smaller value or 1 to request
> specified or bigger value.
>
>
Take another example from alsa-lib/test

Try many parameters but still cannot let alsa-lib/test/latency.c work with
alsa-pulse plugin  and latency stop without any error message

alsa-lib/test/latency -P pulse -C pulse

adding some debug statement and find that it alway fail in setparams()


    if (*bufsize > latency_max) {
+        printf("*bufsize %d > latency_max %d\n",*bufsize,latency_max);
        return -1;
        }