NXP Semiconductors freescale KV4 Series, Reference Manual

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occurs on the last read prior to beginning the write sequence, the write executes using the
data captured during the bus error. If a bus error occurs on the last write prior to
switching to the next read sequence, the read sequence executes before the channel
terminates due to the destination bus error.
A transfer may be cancelled by software with the CR[CX] bit. When a cancel transfer
request is recognized, the DMA engine stops processing the channel. The current read-
write sequence is allowed to finish. If the cancel occurs on the last read-write sequence of
a major or minor loop, the cancel request is discarded and the channel retires normally.
The error cancel transfer is the same as a cancel transfer except the Error Status register
(DMAx_ES) is updated with the cancelled channel number and ECX is set. The TCD of a
cancelled channel contains the source and destination addresses of the last transfer saved
in the TCD. If the channel needs to be restarted, you must re-initialize the TCD because
the aforementioned fields no longer represent the original parameters. When a transfer is
cancelled by the error cancel transfer mechanism, the channel number is loaded into
DMA_ES[ERRCHN] and ECX and VLD are set. In addition, an error interrupt may be
generated if enabled.
NOTE
The cancel transfer request allows the user to stop a large data
transfer in the event the full data transfer is no longer needed.
The cancel transfer bit does not abort the channel. It simply
stops the transferring of data and then retires the channel
through its normal shutdown sequence. The application
software must handle the context of the cancel. If an interrupt is
desired (or not), then the interrupt should be enabled (or
disabled) before the cancel request. The application software
must clean up the transfer control descriptor since the full
transfer did not occur.
The occurrence of any error causes the eDMA engine to stop normal processing of the
active channel immediately (it goes to its error processing states and the transaction to the
system bus still has pipeline effect), and the appropriate channel bit in the eDMA error
register is asserted. At the same time, the details of the error condition are loaded into the
Error Status register (DMAx_ES). The major loop complete indicators, setting the
transfer control descriptor DONE flag and the possible assertion of an interrupt request,
are not affected when an error is detected. After the error status has been updated, the
eDMA engine continues operating by servicing the next appropriate channel. A channel
that experiences an error condition is not automatically disabled. If a channel is
terminated by an error and then issues another service request before the error is fixed,
that channel executes and terminates with the same error condition.
Functional description
KV4x Reference Manual, Rev. 2, 02/2015
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Preliminary
Freescale Semiconductor, Inc.