struct snd_pcm_ops callbacks
Hi,
struct snd_pcm_ops callbacks can be used for sending\receiving PDM audio data to and from a sound card? Or is it only designed for PCM audio data?
On 1/25/23 05:21, Muni Sekhar wrote:
Hi,
struct snd_pcm_ops callbacks can be used for sending\receiving PDM audio data to and from a sound card? Or is it only designed for PCM audio data?
It depends what side of the sound card you are looking at, the physical interface with external devices or the userspace interface.
PDM can be supported at the physical interface level as long as there is a conversion to PCM somewhere in the hardware. Userspace will play/record PCM. See examples in many codecs and SOCs.
There is also the possibility of packing PDM (aka DSD) as pseudo-PCM, that's a trick used by several USB cards. In that case of course the sound card cannot apply any processing to the data and is just a pass-through module.
On Wed, Jan 25, 2023 at 8:30 PM Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com wrote:
On 1/25/23 05:21, Muni Sekhar wrote:
Hi,
struct snd_pcm_ops callbacks can be used for sending\receiving PDM audio data to and from a sound card? Or is it only designed for PCM audio data?
It depends what side of the sound card you are looking at, the physical interface with external devices or the userspace interface.
I am looking at the userspace interface side.
PDM can be supported at the physical interface level as long as there is a conversion to PCM somewhere in the hardware. Userspace will play/record PCM. See examples in many codecs and SOCs.
There is also the possibility of packing PDM (aka DSD) as pseudo-PCM, that's a trick used by several USB cards. In that case of course the sound card cannot apply any processing to the data and is just a pass-through module.
On 1/25/23 12:06, Muni Sekhar wrote:
On Wed, Jan 25, 2023 at 8:30 PM Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com wrote:
On 1/25/23 05:21, Muni Sekhar wrote:
Hi,
struct snd_pcm_ops callbacks can be used for sending\receiving PDM audio data to and from a sound card? Or is it only designed for PCM audio data?
It depends what side of the sound card you are looking at, the physical interface with external devices or the userspace interface.
I am looking at the userspace interface side.
that's not possible without some sort of formatting of 1-bit audio in bytes or more likely 24/32-bit words that look like PCM and can be handled by existing DMA/FIFO hardware. That solution works for HDMI/DP and USB.
PDM can be supported at the physical interface level as long as there is a conversion to PCM somewhere in the hardware. Userspace will play/record PCM. See examples in many codecs and SOCs.
There is also the possibility of packing PDM (aka DSD) as pseudo-PCM, that's a trick used by several USB cards. In that case of course the sound card cannot apply any processing to the data and is just a pass-through module.
participants (2)
-
Muni Sekhar -
Pierre-Louis Bossart