Sony AIT-SDX800, Руководство по техническим характеристикам продукции

Страница: 121 / 204

READ 6.Command Specification
SONY AIT-3Ex drive SDX-800V series Ver.1.0 6-65
6.12.
READ 08h
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (08h)
1 Obsolete Reserved SILI Fixed
2 (MSB)
3 Transfer Length
4 (LSB)
5 Control
READ transfers one or more data blocks to the initiator starting with the next block on the drive.
Fixed: This bit specifies the meaning of the Transfer Length field and whether fixed-length or variable-length blocks
are to be transferred.
If the Fixed bit is set to ZERO, Variable Block mode is requested. A single block is transferred with the Transfer
Length specifying the maximum number of bytes the Host has allocated for the returned data.
If the Fixed bit is set to one, the Transfer Length specifies the number of blocks to be transferred to the Host. This is
valid only if the drive is currently operating in Fixed Block mode, in other words, when it has been instructed to use
fixed-length blocks with MODE SELECT command. If the Fixed bit is set and the drive is in Variable Block mode, the
READ is rejected with a CHECK CONDITION status and an ILLEGAL REQUEST sense key set.
When the Transfer Length is ZERO, no data will be transferred and the current position on the logical unit will not be
changed.
A successful READ command with the Fixed bit set transfers (current Block Length) X (Transfer Length) bytes of
data to the Host. Upon termination of the READ command, the media will be logically positioned after the last block
transferred (EOM side).
SILI: A Suppress Incorrect Length Indicator bit of one indicates that the device will not return CHECK CONDITION
status if the only error is that the Transfer Length is not equal to the actual Block Length recorded on the media.
Note, however, that if the SILI bit is one and the Fixed bit is ZERO, then the device will report CHECK CONDITION,
if the requested Transfer Length is less than the actual block size recorded on the medium (over-length condition)
AND the device is configured to be in Fixed Block mode (i.e. the Block Length field in the MODE SELECT/SENSE
block descriptor is non-ZERO).
If the SILI bit is one and the Fixed bit is one, the drive will terminate the command with a CHECK CONDITION status
with the sense key set to ILLEGAL REQUEST and the additional sense code to ILLEGAL FIELD IN CDB. If the SILI
bit is not set and the actual Block Length is different from the specified transfer length, a CHECK CONDITION status
is returned. Within the Sense data, the Incorrect Length Indicator (ILI) bit and Valid bit will be set to one, the Sense
Key field is set to NO SENSE and the Information Bytes are to set the difference (residue) between the requested
Transfer Length and the actual Block Length, or in Fixed Block mode, the difference (residue) between the
requested number of blocks and the actual number of blocks read. No more than Transfer Length bytes are
transferred to the initiator and the tape is logically positioned after the last block transferred (EOM side).
If the drive reads a File-mark, the drive will return a CHECK CONDITION status. Within the Sense data, the
File-mark and Valid bits are set and the Sense Key field is set to NO SENSE. The information fields contain the
residue count. The Additional Sense Code and Additional Sense Code Qualifier fields are set to File-mark Detected.
Upon termination, the media will be logically positioned after the File-mark (EOM side).
If, however, the drive encounters a Save-Set Mark during a READ, nothing is reported unless the drive has been
configured through MODE SELECT to Report Save-Set Marks. The drive will ignore the Set-mark and continue the
READ. If the Report Save-Set Marks configuration is enabled then the File-mark and Valid bits are set and the
Sense Key field is set to NO SENSE. The information fields contain the residue count and the Additional Sense
Code and Additional Sense Code Qualifier fields are set to Set-mark Detected. The tape is logically positioned after
the Save-Set Mark (EOM side).
If the drive detects EOD during the READ, the drive will return a CHECK CONDITION status. Within the Sense data,
the Valid bit is set and the Sense Key field is set to BLANK CHECK. The information fields contain the residue count.
The Additional Sense Code and Additional Sense Code Qualifier fields are set to EOD DETECTED. Upon
termination, the media will be physically positioned before EOD and after the last block on tape.