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ADSP-BF537 Blackfin Processor Hardware Reference
5-111
Direct Memory Access
Initializing Descriptors in Memory
Descriptor-based DMAs expect the descriptor data to be available in
memory by the time the DMA is enabled. Often, the descriptors are pro-
grammed by software at run-time. Many times, however, the
descriptors—or at least large portions of them—can be static and there-
fore initialized at boot time. How to set up descriptors in global memory
depends heavily on the programming language and the tool set used. The
following examples show how this is best performed in the Vi+
tools’ assembly language.
uses multiple variables of either 16-bit or 32-bit size to
describe DMA descriptors. This example has two descriptors in small list
flow mode that point to each other mutually. At the end of the second
work unit an interrupt is generated without discontinuing the DMA pro-
cessing. The trailing “.end” label is required to let the linker know that a
descriptor forms a logical unit. It prevents the linker from removing vari-
ables when optimizing.
Listing 5-4. Two Descriptors in Small List Flow Mode
.section sdram;
.byte2 arrBlock1[0x400];
.byte2 arrBlock2[0x800];
.section L1_data_a;
.byte2 descBlock1 = lo(descBlock2);
.var descBlock1.addr = arrBlock1;
.byte2 descBlock1.cfg = FLOW_SMALL|NDSIZE_5|WDSIZE_16|DMAEN;
.byte2 descBlock1.len = length(arrBlock1);
descBlock1.end:
.byte2 descBlock2 = lo(descBlock1);
.var descBlock2.addr = arrBlock2;
Содержание Blackfin ADSP-BF537
Страница 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...