8.2.6 SCSI[x] DMA Unaligned Data[1] (DUDx1)—1.8004.1x0C/1.C004.1x0C
The DUDx1 is the buffer for the last 1-3 bytes of unaligned data for DMA writes
to memory. It must be read if the transfer did not end on a longword boundary.
The bytes appear in the correct byte locations. When set to 1, mask bits 24-26
indicate that the corresponding byte contains valid data. Bit three is always
clear.
Save Residual Byte
The 53C94/53CF94-2 transfers a single byte at the end of a transfer if
the transfer count was an odd number and if the save residual byte is
not set. If so, the mask indicates an extra valid byte. If that byte filled a
longword, that longword will be part of a DMA burst.
The register’s format and contents are:
07 0008151624 2331
MR−0102−93RAGS
BYTE[00]BYTE[10] BYTE[01]MASK0000
27 26
Bit Access Reset Description
7:0 R 0 Byte[00]
15:8 R 0 Byte[01]
23:16 R 0 Byte[10]
24 R 0 Mask bit indicating Byte[00] valid
25 R 0 Mask bit indicating Byte[01] valid
26 R 0 Mask bit indicating Byte[10] valid
31:27 R 0 Reserved, read as zero
TURBOchannel Dual SCSI ASIC 8–11
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