Analog Devices ADSP-BF59x Blackfin, Hardware Reference Manual, Page: 196 / 772

Programming Examples
5-96 ADSP-BF59x Blackfin Processor Hardware Reference
.var arrBlock4[N];
.struct dma_desc_list descBlock3 = {
descBlock4, arrBlock3,
FLOW_LARGE | NDSIZE_7 | WDSIZE_32 | DMAEN,
length(arrBlock3), 4,
0, 0 /* unused values */
};
.struct dma_desc_list descBlock4 = {
descBlock3, arrBlock4,
FLOW_LARGE | NDSIZE_7 | DI_EN | WDSIZE_32 | DMAEN,
length(arrBlock4), 4,
0, 0 /* unused values */
};
Software-Triggered Descriptor Fetch Example
Listing 5-7 demonstrates a large list of descriptors that provide
FLOW
= 0
(stop mode) configuration. Consequently, the DMA stops by itself as soon
as the work unit has finished. Software triggers the next work unit by sim-
ply writing the proper value into the DMA configuration registers. Since
these values instruct the DMA controller to fetch descriptors in large list
mode, the DMA immediately fetches the descriptor, thus overwriting the
configuration value again with the new settings when it is started.
Note the requirement that source and destination channels stop after the
same number of transfers. Between stops, the two channels can have com-
pletely individual structures.
Listing 5-7. Software-Triggered Descriptor Fetch
.import "descriptors.h";