Modes of Operation
7-14
ADSP-BF50x Blackfin Processor Hardware Reference
Descriptor-based DMA Operation
In descriptor-based DMA operation, software does not set up DMA
sequences by writing directly into DMA controller registers. Rather, soft-
ware keeps DMA configurations, called descriptors, in memory. On
demand, the DMA controller loads the descriptor from memory and over-
writes the affected DMA registers by its own control. Descriptors can be
fetched from L1 memory using the DCB bus or from external memory
using the DEB bus.
A descriptor describes what kind of operation should be performed next
by the DMA channel. This includes the DMA configuration word as well
as data source/destination address, transfer count, and address modify val-
ues. A DMA sequence controlled by one descriptor is called a work unit.
Optionally, an interrupt can be requested at the end of any work unit by
setting the
DI_EN
bit in the configuration word of the respective
descriptor.
A DMA channel is started in descriptor-based mode by first writing the
32-bit address of the first descriptor into the
DMAx_NEXT_DESC_PTR
register
(or the
DMAx_CURR_DESC_PTR
in case of descriptor array mode) and then
performing a write to the
DMAx_CONFIG
register that sets the
FLOW
field to
either 0x4, 0x6, or 0x7 and enables the
DMAEN
bit. This causes the DMA
controller to immediately fetch the descriptor from the address pointed to
by the
DMAx_NEXT_DESC_PTR
register. The fetch overwrites the
DMAx_CONFIG
register again. If the
DMAEN
bit is still set, the channel starts DMA
processing.
The
DFETCH
bit in the
DMAx_IRQ_STATUS
register tells whether a descriptor
fetch is ongoing on the respective DMA channel. The
DMAx_CURR_DESC_PTR
points to the descriptor value that is to be fetched
next.
Summary of Contents for EZ-KIT Lite ADSP-BF506F
Page 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Page 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...