Sony SDX-800V/R manual Read Buffer 3Ch

6.Command Specification READ BUFFER

6.15.READ BUFFER 3Ch

Bit	7	6	5	4		3	2		1	0
Bite
0				Operation	Code (3Ch)
1		Obsolete		Reserved				Mode
2				Buffer ID
3	(MSB)			Buffer Offset
4
5										(LSB)
6	(MSB)			Allocation Length
7
8										(LSB)
9				Control

READ BUFFER is used in conjunction with WRITE BUFFER as a diagnostic function for testing the data buffer and the SCSI bus integrity of the drive. A REWIND command should be sent to the drive after WRITE/READ BUFFER diagnostic testing to return to normal operation.

Note: This command may not be used to recover data that is buffered within the drive. If the drive receives a READ BUFFER without having had a prior WRITE BUFFER command, only the four byte header will be returned. There is no available data to return, as the drive writes any buffered data to tape prior to accepting either a READ BUFFER or WRITE BUFFER for the first time.

Mode: The drive supports the following values within this field. If any other value is set, the drive will terminate the command with a CHECK CONDITION status and an ILLEGAL REQUEST sense key set.

Table 6-70: READ BUFFER Mode values

Mode	Description
0000b	Combined Header and Data
0010b	Data
0011b	Descriptor
1010b	Echo Buffer
1011b	Echo Buffer Descriptor

Combined Header and Data Mode-in this mode, the drive returns a four-byte header followed by the data bytes. The drive terminates the DATA IN phase when Allocation Length bytes of header plus data have been transferred or when the header and all available data have been transferred to the initiator, whichever is less. The four-byte READ BUFFER header is followed by data bytes from the drive's data buffer.

Table 6-71: READ BUFFER Header

Bit	7	6	5	4		3	2	1	0
Byte
0					Reserved
1	(MSB)			Available Length
2
3									(LSB)

Available Length: 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 - in this mode, the DATA IN phase contains buffer data only.

6-72 SONY AIT-3Ex drive SDX-800V series Ver.1.1