Re: OMAP Audio

[Gary Thomas <gary@mlbassoc.com>]

On 02/17/2010 10:45 AM, Jarkko Nikula wrote:
> On Wed, 17 Feb 2010 05:01:53 -0700
> Gary Thomas<gary@mlbassoc.com>  wrote:
>
>>> After looking at the TRM of OMAP, the sDMA has support for 8, 16 and 32 bit data
>>> types. So I'm not really sure how to configure McBSP and sDMA in case of 24 bit
>>> packed format.
>>> I would go with a trial and error method and find it out how it is working...
>>>
> So it looks that the memory representation must be 32-bit.
>
>> How about sending padded data (24 bits in 32) which is what my
>> CODEC wants anyway?  Would this be easier to set up?  How?
>>
>> (Again, I'm a bit fuzzy on how to tell omap_pcm_prepare that I
>> need to be moving 24 or 32 bit chunks)
>>
> Internal representation and link configuration are separate things:
>
> DMA<->  McBSP rx/tx reg<- [FIFO] ->  McBSP receiver/transmitter
>
> As Peter found, due the DMA and McBSP FIFO, the DMA configuration must
> be 32-bit. But I suppose the McBSP receiver/ransmitter could be
> configured to transmit only 24-bits.
>
> The OMAP35x Applications Processor Multi-Channel Buffered Serial Port
> (McBSP) TRM (SPRUFD1C) seems to have some examples for different data
> lengths than internal word length. Worth to look and try with trial and
> error method using oscilloscope :-)

Thanks.  I'd really like to understand how to set things up to generate
the data I see in TRM:
   Figure 21-11 shows an example with 24 bits data (MSB first) and 8 padding bits at ‘0’.

This matches my CODEC.  Any clues?

BTW, I was able to set things up for 32 bit PCM data, based on
the email thread you pointed at.  Still need the funky 24 bit
stuff though.

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