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Architecture
10.2.8.4.3 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.
10.2.8.4.4 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.
10.2.8.4.5 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.
1052
Multichannel Audio Serial Port (McASP)
Preliminary
© 2011, Texas Instruments Incorporated
www.ti.com
SPRUGX9 – 15 April 2011
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