ADSP-BF50x Blackfin Processor Hardware Reference
7-39
Direct Memory Access
The
HMDMAx_ECINIT
registers reload the
HMDMAx_ECOUNT
registers every time
the handshake mode is enabled (when the
HMDMAEN
bit changes from
0 to 1). If the initial edge count value is 0, the handshake operation starts
with a settled request budget. If positive, the engine starts immediately
transferring the programmed number (up to 32767) of blocks once
enabled, even without detecting any activity on the
DMARx
pins. If nega-
tive, the engine will disregard the programmed number (up to 32768)
significant edges on the
DMARx
inputs before starting normal operation.
Figure 7-3
illustrates how an asynchronous FIFO could be connected. In
such a scenario the
REP
bit should be cleared to let the
DMARx
request pin
listen to falling edges. The Blackfin processor does not evaluate the full
flag such FIFOs usually provide because asynchronous polling of that sig-
nal would reduce the system throughput drastically. Moreover, the
processor first fills the FIFO by initializing the
HMDMAx_ECINIT
register to
1024, which equals the depth of the FIFO. Once enabled, the MDMA
automatically transmits 1024 data words. Afterward it continues to trans-
mit only if the FIFO is emptied by its read strobe again. Most likely, the
HMDMAx_BCINIT
register is programmed to 1 in this case.
In the receive example shown in
Figure 7-4
, the Blackfin processor again
does not use the FIFO’s internal control mechanism. Rather than testing
the empty flag, the processor counts the number of data words available in
the FIFO in its own
HMDMAx_ECOUNT
register. Theoretically, the MDMA
could immediately process data as soon as it is written into the FIFO by
Figure 7-3. Transmit DMA Example Connection
WR
AMSx
1024K x 16 FIFO
BLACKFIN
FF
D0 .. D15
DMARx
RD
I0 .. I15
O0 .. O15
AWE
Summary of Contents for EZ-KIT Lite ADSP-BF506F
Page 50: ...Contents l ADSP BF50x Blackfin Processor Hardware Reference ...
Page 92: ...Development Tools 1 30 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 110: ...Interface Overview 3 12 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 236: ...Internal Flash Memory Control Registers 6 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 650: ...Programming Examples 15 56 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 804: ...Programming Examples 17 92 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1194: ...Programming Examples 24 90 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1256: ...ACM Registers A 50 ADSP BF50x Blackfin Processor Hardware Reference ...
Page 1264: ...Boundary Scan Architecture B 8 ADSP BF50x Blackfin Processor Hardware Reference ...