Reply by laurasscurtu June 3, 20152015-06-03

I am a DSK6713 user and I am interested in knowing how data is received/
transmitted by the McBSP from/to the AIC23 codec.

In the AIC23 data sheet I have read, that in the DSP mode, the LRCIN/
LRCOUT signals are the one who decide when the data transfer starts. When
the LRP bit is set to 0 the LRCIN/LRCOUT signals overlap the MSB. Due to
the fact that the transfer occurs at the falling edge of LRCIN/ LRCOUT, it
means that the MSB is 'lost', sent in the next transfer. 
So the original data may be altered. (Did I understand it correctly???)
When LRP is 1, the MSB is available after the falling edge of the
LRCIN/LRCOUT signal. So the sample is transmitted without any bits loss.

Now, regarding the McBSP part. The clocks and the frame sync signals are
connected to those from the AIC23 codec. In the data sheet it is said that
the internal frame sync signals of the McBSP for receive and transmit must
be active high, and the transmit operation must occur on the rising edge
of the internal clock and the receive operation on the falling edge. 
I have read that the data transfer begins when the FSR is active high.
Does that mean, that the data transfer begins on the rising edge of the
FSR signal? 

I have tried to test how the data transfer occurs for different scenarios
by playing 2 sine signals with different frequencies, each on every
channel, left and right and then separating them by putting 1 sample in
one vector and the consecutive one in anotherone and so on and so forth. 
I have modified the LRP bits of the AIC and the data delay of the McBSP. 
For LRP = 1 and RDATDLY = 1bit / 2 bits it worked fine, but with an
amplitude modification, perhaps because of the bit delays. For LRP = 1 and
RDATDLY = 0 bit it didn't work correctly, thing which I cannot explain
myself, if the data transfer starts when the FSR bit of the McBSP is
active high. Does the FSR bit mask the MSB somehow, or why didn't it work
Similarly, I have modified the LRP to 0 and then put the RDATDLY on 0, 1
and 2. The problem is that I cannot explain myself the behaviour of the
data transfers. 

I would very much appreciate if someone could sum up for me how data is
received / transmitted by the McBSP.

Thanks in advance!




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