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READ BUFFER
7.12. READ BUFFER 3Ch
Bit
7
Byte
0
1
2
3
(MSB)
4
5
6
(MSB)
7
8
9
10
11
READ BUFFER is used in conjunction with the WRITE BUFFER command as a diagnostic function for testing the
buffer bus integrity of the drive. A REWIND command should be sent to the drive after WRITE/READ BUFFER
diagnostic testing to allow 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 the Mode 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.
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 TRANSFER when Allocation Length bytes of header plus data have been
transferred or when the header and all available data have been transferred to the host, whichever is less. The
four-byte READ BUFFER header is followed by data bytes from the drive's data buffer.
Bit
7
Byte
0
1
(MSB)
2
3
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 TRANSFER contains buffer data only.
Descriptor Mode – in this mode a maximum of four bytes of READ BUFFER descriptor information are returned.
The drive returns the descriptor information for the buffer specified by the Buffer ID. In this mode, the drive does
not reject the valid Buffer Ids with a CHECK CONDITION status but returns 3F 68 00h when Buffer ID is set to 0,
80 00 00h when Buffer ID is set to 1 in the READ BUFFER descriptor.
SONY AIT-2 Turbo drive SDX-560V series Ver.1.0
6
5
4
Operation Code (3Ch)
Reserved
Buffer Offset
Allocation Length
Table 7-45: Read Buffer Mode Values
Mode
000b
Combined Header and Data
010b
011b
Table 7-46: Read Buffer Header
6
5
4
Available Length
7. ATAPI Packet Command Specification
3
2
Mode
Buffer ID
Reserved
Reserved
Reserved
Description
Data
Descriptor
3
2
Reserved
1
0
(LSB)
(LSB)
1
0
(LSB)
7-45
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