ADSP-BF537 Blackfin Processor Hardware Reference
5-39
Direct Memory Access
Receive Restart or Finish
No restart or finish control command may be issued by a peripheral to a
channel configured for memory write unless either (a) the peripheral has
already performed at least five DMA transfers in the current work unit, or
(b) the previous work unit was terminated by a finish control command
and the peripheral has performed at least one DMA transfer in the current
work unit. If five data transfers have been performed, then at least one
data item has been written to memory in the current work unit, which
implies that the current work unit’s descriptor fetch completed before the
data grant of the fifth item. Otherwise, if less than five data items have
been transferred, it is possible that all of them are still in the DMA FIFO
and that the previous work unit is still in the process of completion and
transition between work units.
Similarly, if a finish command ended the previous work unit and at least
one subsequent DMA data transfer has occurred, then the fact that the
DMA channel issued the grant guarantees that the previous work unit has
already completed the process of draining its data to memory and transi-
tioning to the new work unit.
Note that if a peripheral terminates all work units with the finish opcode
(effectively assuming responsibility for all work unit boundaries for the
DMA channel), then the peripheral need only ensure that it performs a
single transfer in each work unit before any restart or finish. This requires,
however, that the user programs the descriptors for all work units man-
aged by the channel with
DMAx_CURR_X_COUNT
/
DMAx_CURR_Y_COUNT
s
representing more data items than the maximum work unit size that the
peripheral will encounter. For example,
DMAx_CURR_X_COUNT
/
DMAx_CURR_
Y_COUNT
s of 0 allow the channel to operate properly on 1D work units up
to 65,535 data items and 2D work units up to 4,294,967,295 data items.
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...