Sony SDX-800V, SDX-800V/R

READ BUFFER 6.Command Specification

SONY AIT-3Ex drive SDX-800V series Ver.1.1 6-73

Descriptor Mode - In this mode, a maximum of four bytes of READ BUFFER descriptor information is returned. The

device server shall return the descriptor information for the buffer specified by the BUFFER ID field (see the

description of the buffer ID). If there is no buffer associated with the specified buffer ID, the device server shall return

all zeros in the READ BUFFER descriptor. The BUFFER OFFSET field is reserved in this mode. The allocation

length should be set to four or greater. The device server shall transfer the lesser of the allocation length or four

bytes of READ BUFFER descriptor.

Table 6-72: READ BUFFER Descriptor

Bit

Byte

7 6 5 4 3 2 1 0

0 Reserved

1 (MSB)

2 Buffer Capacity

3 (LSB)

Buffer ID: The supported values are:

Table 6-73:

Buffer ID Description Offset

Read Group Buffer

0 - 0x01000000

0x01000000 - 0x02000000

0x02000000 - 0x03000000

0x03000000 - 0x04000000

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.