User Manual

SCSI Commands Reference Manual, Rev. J 145

www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)

ALLOCATION LENGTH field

If the MODE field is not set to one, the ALLOCATION LENGTH field is defined in 2.2.6.

CONTROL byte

The CONTROL byte is defined in Clause 2.2.7.

3.20.2 Combined header and data mode (00h)

The four-byte READ BUFFER header (see table 105) is followed by data bytes from the buffer.

BUFFER CAPACITY field

The BUFFER CAPACITY field specifies the total number of data bytes available in the buffer. The buffer capacity is not reduced to reflect the

actual number of bytes written using the WRITE BUFFER command with combined header and data mode. The relationship between the BUF-

FER CAPACITY field and the CDB ALLOCATION LENGTH field is defined in 2.2.6. Following the READ BUFFER header, the device server shall

transfer data from the buffer.

3.20.3 Vendor specific mode (01h)

This mode is not supported by Seagate products. If used, the drive will return CHECK CONDITION and report an ILLEGAL

REQUEST/INVALID FIELD IN CDB error.

3.20.4 Data mode (02h)

In this mode, the Data-In Buffer is filled only with logical unit buffer data. The BUFFER ID field specifies a buffer within the logical

unit from which data shall be transferred. Seagate assigns buffer ID codes to buffers within the logical unit. Buffer ID zero shall be

supported. If more than one buffer is supported, then additional buffer ID codes shall be assigned contiguously, beginning with

one. Buffer ID code assignments for the READ BUFFER command shall be the same as for the WRITE BUFFER command. If an

unsupported buffer ID code is selected, then the command shall be terminated with CHECK CONDITION status, with the sense

key set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN CDB.

The BUFFER OFFSET field contains the byte offset within the specified buffer from which data shall be transferred. The

application client should conform to the offset boundary requirements returned in the READ BUFFER descriptor (see 3.20.5). If

the device server is unable to accept the specified buffer offset, the command shall be terminated with CHECK CONDITION

status, with the sense key set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN CDB.

Table 105 READ BUFFER header

Bit

Byte

7 6 5 4 3 2 1 0

0 Reserved

1 (MSB)

BUFFER CAPACITY. . .

3 (LSB)

DATA. . .