Description of Operation
8-18
ADSP-BF537 Blackfin Processor Hardware Reference
RX DMA Data Alignment
If the
RXDWA
bit in the MAC system control register is clear, the MAC
delivers the frame data via DMA to a 32-bit-aligned buffer in memory,
including the Ethernet header and FCS. Because the Ethernet header is an
odd number of 16-bit words long, this results in the frame payload being
odd-aligned, which may be inconvenient for later processing.
If the
RXDWA
bit is set, however, the MAC prefixes one 16-bit pad word to
the frame data with value 0x0000, resulting in a frame payload aligned on
an even 16-bit boundary. See
RX DMA Buffer Structure
The length of each RX DMA buffer must be at least 1556 (0x614) bytes.
This is the maximum number of bytes that the MAC can deliver by DMA
on any receive frame. Frames longer than the 1556-byte hardware limit
Figure 8-6. RX DMA Data Alignment
1
0
DATA BYTE D
EVEN WORD ALIGNMENT, RXDWA = 0
DATA BYTE C
DATA BYTE B
DATA BYTE A
3
2
DATA BYTE H
DATA BYTE G
DATA BYTE F
DATA BYTE E
5
4
DATA BYTE L
DATA BYTE K
DATA BYTE J
DATA BYTE I
1
0
DATA BYTE B
ODD WORD ALIGNMENT, RXDWA = 1
DATA BYTE A
PAD BYTE
PAD BYTE
3
2
DATA BYTE F
DATA BYTE E
DATA BYTE D
DATA BYTE C
5
4
DATA BYTE J
DATA BYTE I
DATA BYTE H
DATA BYTE G
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 ...