Fujitsu MBA3300RC Mode = 0, 0, 1, 1 Buffer descriptor, Read Buffer command buffer descriptor

4.4 Maintenance, Diagnostic Commands

(4) Mode = 0, 0, 1, 1: Buffer descriptor

When this mode is specified, the HDD transfers only the 4-byte buffer descriptor to the INIT. the HDD's data buffer attributes are indicated in the 4-byte buffer descriptor. Zero must be specified in the "Buffer offset" field in the CDB when this mode is specified. The HDD 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.

Table 4.64 READ BUFFER command: buffer descriptor

	Bit	7	6	5	4	3	2	1	0
Byte
0				X'02' Addressing Boundary
1		(MSB)
2					Buffer Capacity
3									(LSB)

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 HDDs report X'02' (=22), indicating that it is possible to specify the address in 4-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.

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.

(5) Mode = 1, 0, 1, 0 : Echo buffer

In this mode the HDD transfers data to the INIT from the echo buffer. The echo buffer shall transfer the same data as when the WRITE BUFFER command with the mode field set to echo buffer was issued. The BUFFER ID and BUFFER OFFSET fields are ignored in this mode.

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