Functional Description
5-38
ADSP-BF537 Blackfin Processor Hardware Reference
•
Request Data Urgent
The request data urgent control command behaves identically to
the DMA request control command, except that while it is asserted
the DMA channel performs its memory accesses with urgent prior-
ity. This includes both data and descriptor-fetch memory accesses.
A DMA-management-capable peripheral might use this control
command if an internal FIFO is approaching a critical condition,
for example.
Restrictions
The proper operation of the 4-location DMA channel FIFO leads to cer-
tain restrictions in the sequence of DMA control commands.
Transmit Restart or Finish
No restart or finish control command may be issued by a peripheral to a
channel configured for memory read unless both (a) the peripheral has
already performed at least one DMA transfer in the current work unit, and
(b) the current work unit has more than four items remaining in
DMAx_
CURR_X_COUNT
/
DMAx_CURR_Y_COUNT
(thus not yet read from memory.)
Otherwise, the current work unit may already have completed memory
operations and can no longer be restarted or finished properly.
If the
DMAx_CURR_X_COUNT
/
DMAx_CURR_Y_COUNT
of the current work unit is
sufficiently large that it is always at least 5 more than the maximum data
count prior to any restart or finish command, the above restriction is satis-
fied. This implies that any work unit which might be managed by restart
or finish commands must have
DMAx_CURR_X_COUNT
/
DMAx_CURR_Y_COUNT
values representing at least 5 data items.
Note in particular that if the
DMAx_CURR_X_COUNT
/
DMAx_CURR_Y_COUNT
reg-
isters are programmed to 0 (representing 65,536 transfers, the maximum
value) the channel will operate properly for 1D work units up to 65,531
data items or 2D work units up to 4,294,967,291 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 ...