[alsa-devel] What is the meaning of the mask values in the pcmhw constraints struct ?

Neil Jones neil.jones at imgtec.com
Fri Oct 23 15:39:58 CEST 2009

>> I get the error "aplay: set_params:1022: Unable to install hw
>> I have traced the problem to a failing ioctl call
>> (snd_pcm_playback_ioctl) the error occurs in snd_pcm_hw_refine when
>> refining the mask for the SNDRV_PCM_HW_PARAM_ACCESS mask, all the bit
>> fields in my runtime->hw_constraints are zero for this field, but the

>You should set these up with snd_soc_set_runtime_hwparams() with the
>flags in the info field.

>> requested params have the value 7, Im not sure what this means, the
>> SNDRV_PCM_ACCESS_xxx defines in asound.h only go upto 4 ?

>It's a bitmask at this point, treat those values as shifts.

Cheers, I wasn't setting the 'SNDRV_PCM_INFO_MMAP' in my
snd_pcm_hardware description, because I didn't have MMAP support, I have
now added MMAP support to my driver to resolve this issue, although I
thought ALSA/aplay supported drivers without MMAP support ?

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