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6. COMMAND SPECIFICATION
Bit
7
Byte
0
1
(MSB)
2
3
Available Length:
Specifies the total number of data bytes that are available in the target'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 target will transfer data from its data buffer.
Data Mode - In this mode, the DATA IN phase contains buffer data only.
Descriptor Mode - In this mode a maximum of four bytes of READ BUFFER descriptor information are returned. The
drive returns the descriptor information for the buffer specified by the Buffer ID. In this mode, the drive does not
reject the valid Buffer IDs with a CHECK CONDITION status but returns 1F F8 00h when Buffer ID is set to 0, 80
00 00h when Buffer ID is set to 1 in the READ BUFFER descriptor.
Bit
7
Byte
0
1
(MSB)
2
3
Buffer ID:
The drive supports Buffer ID field of zero and one. If the Buffer ID is set to ZERO, the initiator has access to the I/
F Buffer. If the Buffer ID is set to ONE, the initiator has access to the Group Buffer.
Buffer Offset:
The buffer offset field contains the byte offset within the specified buffer from which data shall be transferred from.
The initiator should conform to the offset boundary requirements returned in the READ BUFFER descriptor. If the
target is unable to accept the specified buffer offset, it shall return CHECK CONDITION status, shall set the Sense
Key to ILLEGAL REQUEST, and set the Additional Sense Code to ILLEGAL FIELD IN CDB.
Allocation Length:
The Allocation Length specifies the maximum number of bytes that the initiator has allocated for returned data. An
Allocation Length of zero indicates that no data will be transferred. Any other value indicates the maximum number
of bytes that will be transferred. The drive terminates the DATA IN phase when Allocation Length bytes of data
have been transferred or when all available data has been transferred to the initiator, whichever is less. The Alloca-
tion Length must be greater than four (except in data only mode), else the drive will return a CHECK CONDITION
status with an ILLEGAL REQUEST sense key set.
6 - 60
SONY SDT-10000/SDT-11000 DDS Tape Drive
6
5
4
Available Length
Table 6-39: READ BUFFER Header
6
5
4
Buffer Capacity
Table 6-40: READ BUFFER Descriptor
3
2
Reserved
3
2
Reserved
READ BUFFER
1
0
(LSB)
1
0
(LSB)
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