[alsa-devel] [PATCH 1/4] ASoC: pxa-ssp: enhance I2S and add Left_J support

[Daniel Ribeiro]

Hi Eric,

Em Ter, 2009-06-09 às 17:39 +0800, Eric Miao escreveu:
> frame_width = sample_width * channel ( = LRCLK for I2S )
> 
> is no longer (and ever) correct.
> 
> E.g. the frame width could be 64fs, meaning a whole frame is
> consisting
> of 64 bitclks - that's saying, sample width from 1 - 64 are possible,
> For typical 16-bit sample width I2S format, the envelope for each
> sample
> is 32 bitclks, and offseting by 1 bitclk starts the 16-bit sample.

I'm working on supporting I2S right now, and I found some issues with
this enveloping thing.

First, it doesn't work on pxa2xx. DMYSTOP on pxa2xx is only 0-3.

Second, is enveloping needed at all? The patch you sent supports 32bits
frames for 2*16bits samples or 64bits frames for 2*32bits samples using
FSRT.

We already use FSRT for DSP_A, and if this works on littleton I2S we
should just stick with FSRT (and frame_width = sample_width * channels)
to keep the code simple.

> And the TDM mode is actually special for PXA-SSP to emulate the I2S
> protocol, it's no way generic TDM in a common sense. So talking about
> set_tdm_slots(), I'd really like to hide into the format setting code
> of I2S/Left_J to avoid further confusion.

TDM is needed for frames larger than 32 bits on any dai format. Its not
something specific to I2S.

-- 
Daniel Ribeiro
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