Re: OMAP Audio

[Gary Thomas <gary@mlbassoc.com>]

On 02/17/2010 03:26 AM, Peter Ujfalusi wrote:
> On Wednesday 17 February 2010 09:03:39 ext Jarkko Nikula wrote:
>> On Tue, 16 Feb 2010 11:19:25 -0700
>>
>> Gary Thomas<gary@mlbassoc.com>  wrote:
>>> I need to connect the OMAP (3530) to a 24bit CODEC.  So far
>>> my attempts at getting this to go have not gone well.  Then
>>>
>>> I ran across this comment in sound/soc/omap/omap-pcm.c:
>>> 	/*
>>> 	
>>> 	 * Note: Regardless of interface data formats supported by OMAP McBSP
>>> 	 * or EAC blocks, internal representation is always fixed 16-bit/sample
>>> 	 */
>>>
>>> Does this mean that this setup is just not supported?  even though
>>> the hardware can handle it?
>>
>> Yep, comment is bit misleading but true until some patch will remove
>> it. IRCC, the EAC was limited to 16-bit and also there wasn't need and
>> HW to test other formats than S16_LE in McBSP DAI.
>>
>>> Thanks for any pointers or ideas on how to get this going.
>>
>> I would first start adding support for the S32_LE into omap-pcm.c (DMA
>> part). Worth to look this thread:
>>
>> http://mailman.alsa-project.org/pipermail/alsa-devel/2010-January/024704.ht
>> ml
>>
>> Then add support for this format to the omap-mcbsp.c (link
>> configuration part).
>>
>> Next step would be to add support for the S24_LE on 4-byte boundaries.
>> I.e. the DMA is moving 32-bit samples between the memory and McBSP but
>> only 24-bits are transferred over the McBSP and codec.
>
> Hmmm, I think this is a bit more complicated than that at least on OMAP3.
> I think the DMA engine should also move 24 bit words.
> This is dictated by the McBSP FIFO: it has a notion of word size, and it is
> expecting that the DMA engine will move THRESHOLD number of words. So if the
> McBSP is configured for 24 bit words, than the DMA word size has to match that.
>
> Apart from this, the constraint set for the period bytes need to be changed
> since as you change the word size in McBSP you will have different amount of
> actual bytes for the FIFO (the FIFO size is in words, and the maximum word size
> is 32 bit).
>

Thanks for the help.  I'm pretty sure I understand how to change
the McBSP code (omap-mcbsp.c) to handle the various formats, but
I'm a bit lost in the DMA setup (omap-pcm.c).  How do I identify
the code/width in omap_pcm_prepare()?

Has no one ever used the OMAP/McBSP with data sizes other than 16 bits??

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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