On 02/17/2010 10:45 AM, Jarkko Nikula wrote:
On Wed, 17 Feb 2010 05:01:53 -0700
Gary Thomas<gary@xxxxxxxxxxxx> 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.
--
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Gary Thomas | Consulting for the
MLB Associates | Embedded world
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