Analog Devices ADSP-BF535 Blackfin, Hardware Reference Manual

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ADSP-BF535 Blackfin Processor Hardware Reference 9-15
Direct Memory Access
Autobuffer Based DMA
Autobuffer based DMA operates like descriptor based DMA except that it
does not require descriptors in memory. In autobuffer mode, DMA con-
trol registers are writable and programmed directly by the processor to
initiate a DMA transfer sequence. Upon completion of the transfer
sequence, the control registers are reloaded with their original setup values
for the next transfer. This effectively creates a circular buffer that contin-
ues to transfer data until disabled by clearing the DMA Enable bit in the
peripheral’s DMA Configuration register. If enabled, interrupts are gener-
ated at the halfway and completion points in the transfer sequence. For
more information about peripheral interrupts, see the appropriate periph-
eral chapter.
Setting Up Autobuffer Based DMA
The following steps illustrate the typical sequence for setting up autobuf-
fer based DMA.
1. Set the Autobuffer Enable bit in the DMA Configuration register.
2. Initialize the DMA Transfer Count, DMA Start Address High, and
DMA Start Address Low registers.
3. Write to the DMA Configuration register, configuring the DMA
transfer and setting the DMA Enable bit.
This final write starts the autobuffer based DMA transfer sequence.

To disable autobuffering, clear the DMA Enable bit in the Config-
uration register. Clearing the bit during active operation will stop
the current single or burst transfer, but it will not cause a DMA
error abort as it would for descriptor based DMA. The Autobuffer
Enable bit in the DMA Configuration register can then be cleared.