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(4)
Mode = 0, 1, 1: Buffer Descriptor
When this mode is specified, the IDD transfers only the 4-byte buffer descriptor to the INIT.
the IDD's data buffer attributes are indicated in the 4-byte buffer descriptor. Zero must be
specified in the "Buffer address" field in the CDB when this mode is specified. The IDD
transfers the data length specified in the "Transfer byte length" field in the CDB or 4 bytes,
whichever portion of data is smaller, to the INIT. When zero is specified in the "Transfer byte
length" field, this command is terminated without executing a data transfer.
Bit
Byte
0
1
2
3
Figure 3. 33 READ BUFFER Command: Buffer Descriptor
The "Addressing boundary" field in the buffer descriptor indicates the addressing boundary in
the data buffer which can be specified in the WRITE BUFFER Command and the READ
BUFFER Command as a "Power" when expressed as a "Power of 2." The IDD reports X '01'
1
(=2
), indicating that it is possible to specify the address in 2-byte units. Also, the "Buffer
capacity" field indicates the byte length of the size of the data buffer which can be operated by
the WRITE BUFFER and READ BUFFER commands.
Note: Exercise caution regarding the following points when using this command.
If the WRITE BUFFER command or READ BUFFER command is used under a multi-
initiator or multitask environment, it is necessary to be careful of the contents of the data
buffer being changed by another initiator or a command that issues another task during the
interval between completion of WRITE BUFFER command execution and execution of
the READ BUFFER command. In order to avoid this problem, it is necessary either to
issue the commands with the READ BUFFER command linked to the WRITE BUFFER
command or, in the case of a multi-initiator environment, to reserve the IDD by the
RESERVE UNIT command.
3 - 130
7
6
5
X'01'
Addressing Boundary
X'07'
Buffer Capacity (MSB)
X'F8' Buffer Capacity
X'00'
Buffer Capacity (LSB)
C141-E039-01EN
4
3
2
1
0
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