Descriptor-Based Dma Operation - Analog Devices Blackfin ADSP-BF537 Hardware Reference Manual

Modes of Operation
This produces the following address offsets from the start address:
0,1,2,...15,
N,N + 1, ... N + 15,
2N, 2N + 1,... 2N + 15, ...
7N, 7N + 1,... 7N + 15,
Example 2: Receive a video datastream of bytes,
(R,G,B pixels) × (N × M image size):
DMAx_X_MODIFY = (N * M)
DMAx_X_COUNT = 3
DMAx_Y_MODIFY = 1 – 2(N * M) (negative)
DMAx_Y_COUNT = (N * M)
This produces the following address offsets from the start address:
0, (N * M), 2(N * M),
1, (N * M) + 1, 2(N * M) + 1,
2, (N * M) + 2, 2(N * M) + 2,
...
(N * M) – 1, 2(N * M) – 1, 3(N * M) – 1,

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.
5-16 ADSP-BF537 Blackfin Processor Hardware Reference