Section 5 SCSI Programming Guidelines
The function
of
this command and the meaning
of
the allocation length field depend on the contents
of
the
mode field. The mode field is defined as follows:
Bit2
Bitt
BitO
MODE
0 0 0 Read combined header and data
0
0
1
Vendor unique
0 1
0 Read
data
0 1
1
Not supported
1
0 0 Reserved
1
0 1 Reserved
1 1 0 Reserved
1
1 1
Reserved
5.11.24.1 COMBINED HEADER AND DATA Mode
(OOOal
In this mode. header and data bytes are returned to the initiator during the
OAT
A IN phase. A four-byte
READ
BUFFER header (Table 5-44) is followed by data bytes from the ProDrive'data buffer. The
specified allocation length (bytes 6-8) must account for both header and data bytes. The ProDrive
terminates the DA T A IN phase when the allocated number
of
bytes
of
header plus data have been transferred
or when all available header and data have been transferred to the initiator. whichever occurs first.
TABLE
5-44
READ
BUFFER Header
Bit
7
6
5
4
3 2 1
o
Byte
o RESERVED
1-3
(MSB)
A
VAll..ABLE
LENGTH
AVAILABLE
LENGTH
(Bytes 1-3) - Specifies the total number
of
data bytes available in the
drive's data buffer. This number is not reduced to reflect the allocation length nor is it reduced to
reflect the actual number
of
bytes written using the WRITE BUFFER command. Following the
READ
BUFFER header, the ProDrive will transfer data from its data buffer. The number
of
data
bytes transferred following the READ
BUFFER header will be the allocation length minus four
or
64K bytes. whichever is less.
5.11.24.2 VENDOR UNIQUE Mode (00181
Not used by ProDrive.
5.11.24.3 DATA Mode (01081
In this mode, the DATA IN phase contains buffer data only. The ProDrive terminates the DATA IN
phase when the allocated number
of
bytes
of
data have been transferred
or
when all data have been transferred
to the initiator, whichever occurs first.
5-68
SCSI
Programming
Guidelines
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