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

[Eric Miao]

On Tue, Jun 9, 2009 at 5:39 PM, Eric Miao <eric.y.miao at gmail.com> wrote:
>
>
> 2009/6/9 Daniel Ribeiro <drwyrm at gmail.com>:
> > Em Seg, 2009-06-08 às 19:06 +0100, Mark Brown escreveu:
> >> Think about TDM mode for a minute here - there a separate configuration
> >> for the sample size on the wire opens the way to using a lower sample
> >> size in a given timeslot than the timeslot supports, reducing the need
> >> for the CPU to rewrite data.  Or to put it another way, I can't see TDM
> >> mode working unless the sample size is constrained to always be exactly
> >> that desired so it seems sensible to have a standard way of doing that.
> >
> > Hum... Now I understood this. If i want to use network mode with 2
> > different codecs, and they differ on the expected frame_size i have to
> > use the smaller frame_size for both codecs.
> >
> > And indeed, in this case the best place to setup the frame size would be
> > on set_tdm_slot().
> >
> >> I'd rather come up with a cleaner way of configuring the magician case
> >> that's explicit about what it's trying to achieve.  It doesn't need to
> >> be in user space, though.
> >
> > I dont know how to do this other than just changing the frame size... :)
> >
>
> OK, not having enough time to read all this thread, let's make sure
> first we are on the same floor:
>
> frame_width  = number of bit clocks per frame
> sample_width = number of bits per sample
>
> And the assumption that
>
> 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,

sorry for the HTML mail, and here is a typo: sample width should be within 1-32

> 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.
>
> 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.
>
> And I still didn't quite capture the issue of magician. Phillip, do
> you have any HW reference to the audio codec and the connection on
> magician?



--
Cheers
- eric