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READ BUFFER 6.Command Specification
SONY AIT-5 drive SDX-1100V series Ver.1.0 6-71
Table 6-73: READ BUFFER Header
Bit
Byte
7 6 5 4 3 2 1 0
0 Reserved
1 (MSB)
2 Available Length
3 (LSB)
Available Length: This field specifies the total number of data bytes that are available in the target's data buffer.
This number is not reduced to reflect the Allocation Length nor is it reduced to reflect the actual number of bytes
written using the WRITE BUFFER command. Following the READ BUFFER header, the target will transfer data
from its data buffer.
Data Mode (0010b) - in this mode, the DATA-IN phase contains buffer data only. The Buffer ID field identifies a
specific buffer within the logical unit from which data will be transferred.
Buffer ID: The supported values are:
Table 6-74: Buffer ID values
Buffer ID Description Offset
0
80
81
82
83
Read Group Buffer
Read Group Buffer
Read Group Buffer
Read Group Buffer
Read Group Buffer
0 - 0x01000000
0 - 0x01000000
0x01000000 - 0x02000000
0x02000000 - 0x03000000
0x03000000 - 0x03700000
If an unsupported Buffer ID code is requested, the drive returns a CHECK CONDITION status with an ILLEGAL
REQUEST sense key set.
Descriptor Mode (0011b) - In this mode, a maximum of four bytes of READ BUFFER descriptor information is
returned. The drive will 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 drive will return all
zeros in the READ BUFFER descriptor. The BUFFER OFFSET field is reserved in this mode. The allocation length
will be set to four or greater. The drive will transfer the lesser of the allocation length or four bytes of READ
BUFFER descriptor.
Table 6-75: READ BUFFER Descriptor
Bit
Byte
7 6 5 4 3 2 1 0
0 Reserved
1 (MSB)
2 Buffer Capacity
3 (LSB)
Buffer Capacity: This field returns the size of the selected buffer in bytes.
Read Data from Echo Buffer (1011b) - 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.
Note: Refer to INCITS TR-28-2002 regarding the Domain Validation.