Description of Operation
8-12
ADSP-BF537 Blackfin Processor Hardware Reference
Receive DMA works with a queue or ring of DMA descriptor pairs struc-
tured as data and status.
•
Data
– The first descriptor in each pair points to a data buffer that
is at least 1556 (0x614) bytes long and is 32-bit aligned. The
descriptor
XCOUNT
field should be set to 0, because the MAC con-
trols the actual buffer length.
•
Status
– The second descriptor points to a status buffer of either 4
or 8 bytes. The descriptor
XCOUNT
field should be set to 0, because
the MAC controls the actual buffer length. After receiving and
accepting any RX frame, the MAC writes a status word and option-
ally two IP checksum words to this status buffer. The
RXCKS
bit in
the
EMAC_SYSCTL
register controls the generation of the two check-
sum words.
Status words written by the MAC after frame reception have the
same format as the current RX frame status register, and always
have the receive complete bit set to 1. If the driver software initial-
izes the length/status words to 0, it can reliably interrogate (poll)
an RX frame’s length/status word to determine if the DMA transfer
of the data buffer is complete. Alternatively, status descriptors may
be individually enabled to signal an interrupt when frame reception
is complete.
The MAC and DMA operate on the active queue in this manner:
•
Start
– The queue is activated by initializing the DMA next
descriptor pointer and then writing the
DMA_CONFIG
register. Mean-
while, the MAC listens to the MII, looking for a frame that passes
its address filter.
•
Data
– When a matching frame is seen, the MAC transfers the
frame data into the data buffer. The MAC does not initiate the
DMA transfer until either the destination address filtering is com-
plete, or the frame ends (if a runt frame).
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 ...