[alsa-devel] ASoC: how to calculate dma size in tdm mode
Hi Mark,
If user app use 2 channels but codec need 8 channels in tdm mode, I need to copy this data from user space to dma buffer. I wonder how to calculate dma size, snd_pcm_hardware.buffer_bytes_max or buffer_bytes_max * tdm_channels / channels_min?
Thanks, Scott
On Thu, Aug 09, 2012 at 05:56:57PM +0800, Scott Jiang wrote:
If user app use 2 channels but codec need 8 channels in tdm mode, I need to copy this data from user space to dma buffer. I wonder how to calculate dma size, snd_pcm_hardware.buffer_bytes_max or buffer_bytes_max * tdm_channels / channels_min?
I'm not sure which data you mean here? It sounds like your hardware doesn't support stereo DMA, if that's the case your capabilites should reflect it. With most hardware you'd just do a normal stereo playback here, the unused TDM timeslots would not be visible outside of the DAI.
2012/8/9 Mark Brown broonie@opensource.wolfsonmicro.com:
On Thu, Aug 09, 2012 at 05:56:57PM +0800, Scott Jiang wrote:
If user app use 2 channels but codec need 8 channels in tdm mode, I need to copy this data from user space to dma buffer. I wonder how to calculate dma size, snd_pcm_hardware.buffer_bytes_max or buffer_bytes_max * tdm_channels / channels_min?
I'm not sure which data you mean here? It sounds like your hardware doesn't support stereo DMA, if that's the case your capabilites should reflect it. With most hardware you'd just do a normal stereo playback here, the unused TDM timeslots would not be visible outside of the DAI.
I'm not sure what stereo DMA mean. Our hardware supports mask that choose which slot is active,but I can't solve the problem that app channel order is different from that required by codec. For example, app is 1L1R2L2R, ad1836 requires 1L2Lxx1R2Rxx. So I choose to copy one by one.
participants (2)
-
Mark Brown -
Scott Jiang