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6.Command Specification
Bit
7
Byte
0
1
(MSB)
2
3
Buffer ID: The supported values are:
If an unsupported Buffer ID code is requested, the drive returns a CHECK CONDITION status with an ILLEGAL
REQUEST sense key set.
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 Allocation 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.
Read Data from Echo Buffer: Domain Validation is an important feature introduced in Ultra160 SCSI. It provides a
mechanism for SCSI devices to perform at maximum possible operational data transfer speed. Domain validation
performs a quick test to help ensure an initiator and target can actually transfer data at negotiated speeds. Using
Echo Buffer option, the initiator can do a more extensive data transfer validation test. The initiator transmits the data
using the WRITE BUFFER command with the echo buffer option and requests it back using the READ BUFFER
command with echo buffer option.
Echo Buffer (1010b): In this mode the drive transfer data to the application client 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. The READ BUFFER command
shall return the same number of bytes of data as received in the prior echo buffer mode WRITE BUFFER command
from the same initiator.
The initiator may send a READ BUFFER command requesting the echo buffer descriptor prior to a WRITE BUFFER
command. If an echo buffer mode WRITE BUFFER command is successful then the initiator may send multiple echo
buffer mode READ BUFFER commands to read the echo buffer data multiple times.
Echo buffer descriptor (1011b): In this mode, a maximum of four bytes of READ BUFFER descriptor information is
returned. The drive will return the descriptor information for the echo buffer. The BUFFER OFFSET field is reserved
in this mode. The allocation length should be set to four or greater.
Bit
7
Byte
0
1
2
3
6-70
Table 6-60: READ BUFFER Descriptor
6
5
Buffer ID
0
Read Interface Buffer
1
Read Group Buffer
Echo Buffer descriptor
6
5
Reserved
Reserved
4
3
2
Reserved
Buffer Capacity
Description
4
3
2
Reserved
(MSB)
SONY AIT-2 Turbo drive SDX-550V series Ver.1.0
READ BUFFER
1
0
(LSB)
1
0
EBOS (1)
BUFFER CAPACITY (LSB)
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