6.Command Specification | REQUEST SENSE |
6.22.REQUEST SENSE 03h
Bit | 7 | 6 | 5 | 4 |
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0 |
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| Operation | Code (03h) |
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1 |
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2 |
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3 |
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4 |
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| Allocation Length (1Ch) |
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5 |
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| Control |
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The REQUEST SENSE command requests that the target transfer Sense Data to the initiator.
The Sense Data will be valid for a CHECK CONDITION status returned on the previous 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 28 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 ASC/ ASCQ 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 initiator 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 initiator requires the exact physical positioning of the media, it will precede the REQUEST SENSE with a WRITE FILEMARKS command with the number of Filemarks field = 0 and with the immediate bit set to ZERO. 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.
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 transferred to the initiator, whichever is less.
The returned sense information has the following format:
SONY |
