
ADSP-BF59x Blackfin Processor Hardware Reference
5-37
Direct Memory Access
stalling the EBIU accesses by the
ARDY
signal. Nevertheless, the peripheral
may request a block transfer before the entire buffer is available by simply
taking the minimum transfer time based on wait-state settings into
consideration.
The block count defines how many data transfers are performed by
the MDMA engine. A single DMA transfer can cause two read or
write operations on the EBIU port if the transfer word size is set to
32-bit in the
MDMA_yy_CONFIG
register (
WDSIZE
= b#10).
Since the block count registers are 16 bits wide, blocks can group up to
65,535 transfers.
Once a block transfer has been started, the
HMDMAx_BCOUNT
registers return
the remaining number of transfers to complete the current block. When
the complete block has been processed, the
HMDMAx_BCOUNT
register returns
zero. Software can force a reload of the
HMDMAx_BCOUNT
from the
HMDMAx_BCINIT
register even during normal operation by setting the
RBC
bit in the
HMDMAx_CONTROL
register. Set
RBC
when the HMDMA module is
already active, but only when the MDMA is not enabled.
Pipelining DMA Requests
The device mastering the DMA request lines is allowed to request addi-
tional transfers even before the former transfer has completed. As long as
the device can provide or consume sufficient data it is permitted to pulse
the
DMARx
inputs multiple times.
The
HMDMAx_ECOUNT
registers are incremented every time a significant edge
is detected on the respective
DMARx
input, and they are decremented when
the MDMA completes the block transfer. These read-only registers use a
16-bit twos-complement data representation: if they return zero, all
requested block transfers have been performed. A positive value signals up
to 32767 requests that haven’t been served yet and indicates that the
MDMA is currently processing. Negative values indicate the number of
Summary of Contents for ADSP-BF59x Blackfin
Page 64: ...Development Tools 1 22 ADSP BF59x Blackfin Processor Hardware Reference...
Page 74: ...Processor Specific MMRs 2 10 ADSP BF59x Blackfin Processor Hardware Reference...
Page 244: ...Programming Examples 6 40 ADSP BF59x Blackfin Processor Hardware Reference...
Page 700: ...Programming Examples 16 78 ADSP BF59x Blackfin Processor Hardware Reference...
Page 738: ...Boundary Scan Architecture B 8 ADSP BF59x Blackfin Processor Hardware Reference...