On Tue, 2010-10-19 at 17:48 -0500, pl bossart wrote:
As this is used to transfer speech frames from/to cellular modem that have specific timing constraints (and modem also uses the I2S path to send some side-info), the Alsa SoC interface cannot be used.What makes you say this? You have provided no detail on what problems you believe exist and since ASoC is a *very* thin wrapper around the core ALSA for DMA stuff it is very surprising that you would see any issues here that don't also affect plain ALSA. If there are any issues then it would seem better to resolve these within the current framework rather than completely discarding the entire existing infrastructure.
Louis meant ALSA rather than ASOC. We use burst transfers to reduce round-trip delay, the whole notion of periods/period elapsed/ring buffer doesn't make sense here and there is in-band signalling that should not be interpreted as samples. If ALSA had a simplified API for byte streams sent over a serial output, we would have no problems using it and of course ASOC would be used then.
Is the inband signaling here done in software ? I'd expect this to be multiplexed in the DAI by the hardware leaving the software to send PCM bursts to the CODEC/MODEM/whatever like Peter's DAC33 driver.
Liam