Sony DDS-4, Руководство по описанию продукции

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6 - 75 SONY SDT-10000/SDT-11000 DDS Tape Drive
6. COMMAND SPECIFICATION
Bit 7 6 5 4 3 2 1 0
Byte
0 Operation Code (03h)
1 Logical Unit Number Reserved
2 Reserved
3 Reserved
4 Allocation Length (1Ch)
5 Unused (00b) Reserved
6. 19 REQUEST SENSE 03h
REQUEST SENSE
The REQUEST SENSE command requests that the target transfer sense data to the initiator.
The Sense Data will be valid for a CHECK CONDITION or RESERVATION CONFLICT status returned on the previ-
ous command. The Sense data will be preserved by the target until retrieved by the REQUEST SENSE command or
until the receipt of any other command from the same initiator. The 26 bytes of Sense data are cleared upon receipt of
any subsequent command to the logical unit, including another REQUEST SENSE.
If the drive receives an unsolicited REQUEST SENSE, then it returns Sense data with the Filemark, EOM and the
appropriate values in the Additional Sense Code/Additional Sense Code Qualifier fields. These fields are only set if the
drive is currently logically positioned at BOM/P, EOM, EOD, or after a Filemark or after a Setmark. The Host is
required to know what the current direction of tape motion is and, therefore to know whether the logical position at a
Filemark or Setmark is either on the BOT or EOT side of that mark.
The positional information provided reflects the logical position of the drive. The drive returns information based on the
data still in its buffer as well as the data on tape.
The REQUEST SENSE command does not cause the drive to flush its buffered data to tape. Therefore, if the Host
requires the exact physical positioning of the media, it should precede the REQUEST SENSE with a WRITE
FILEMARKS command with the number of Filemarks field = 0 and with the immediate bit set to 0. This command will
force the drive to flush any currently buffered data to tape. A subsequent REQUEST SENSE will return the initiator the
actual physical (and logical) position of the drive.
Note: The drive will only maintain valid positional information on normal operating commands. If the SEND DIAG-
NOSTIC or READ/WRITE BUFFER commands are sent to the drive, valid positional information will not be
returned in response to an unsolicited REQUEST SENSE.
Allocation Length:
The Allocation Length specifies the maximum number of sense bytes to be returned. The drive terminates the
transfer when the Allocation Length bytes have been transferred or when all available sense data has been trans-
ferred to the Host, whichever is less.