Functional Description
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22.3.10.4.3 Buffer Overrun Error - Receiver
A buffer overrun can only occur for serializers programmed to be receivers. A buffer overrun occurs when
the serializer is instructed to transfer data from XRSR[n] to XRBUF[n], but XRBUF[n] has not yet been
read by either the DMA or the processor. When this occurs, the receiver state machine sets the ROVRN
flag. However, the individual serializer writes over the data in the XRBUF[n] register (destroying the
previous sample) and continues shifting.
An overrun is checked only once per time slot. The ROVRN flag is set when an overrun condition occurs.
It is possible that an overrun occurs on one time slot but then the processor catches up and does not
cause an overrun on the following time slots. However, once the ROVRN flag is set, it remains set until
the processor explicitly writes a 1 to the ROVRN bit to clear the ROVRN bit.
22.3.10.4.4 DMA Error - Transmitter
A transmit DMA error, as indicated by the XDMAERR flag in the XSTAT register, occurs when the DMA
(or CPU) writes more words to the DAT port of the McASP than it should. For each DMA event, the DMA
should write exactly as many words as there are serializers enabled as transmitters.
XDMAERR indicates that the DMA (or CPU) wrote too many words to the McASP for a given transmit
DMA event. Writing too few words results in a transmit underrun error setting XUNDRN in XSTAT.
While XDMAERR occurs infrequently, an occurrence indicates a serious loss of synchronization between
the McASP and the DMA or CPU. You should reinitialize both the McASP transmitter and the DMA to
resynchronize them.
22.3.10.4.5 DMA Error - Receiver
A receive DMA error, as indicated by the RDMAERR flag in the RSTAT register, occurs when the DMA (or
CPU) reads more words from the DAT port of the McASP than it should. For each DMA event, the DMA
should read exactly as many words as there are serializers enabled as receivers.
RDMAERR indicates that the DMA (or CPU) read too many words from the McASP for a given receive
DMA event. Reading too few words results in a receiver overrun error setting ROVRN in RSTAT.
While RDMAERR occurs infrequently, an occurrence indicates a serious loss of synchronization between
the McASP and the DMA or CPU. You should reinitialize both the McASP receiver and the DMA to
resynchronize them.
3810
Multichannel Audio Serial Port (McASP) SPRUH73H–October 2011–Revised April 2013
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