READ | 6.Command Specification |
6.12.READ 08h
Bit | 7 | 6 | 5 |
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| Operation | Code (08h) |
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1 |
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| SILI | Fixed | |
2 | (MSB) |
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| Transfer Length |
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4 |
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5 |
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| Control |
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The READ command requests that the target transfer 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
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 initiator 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 initiator. This is valid only if the drive is currently operating in Fixed Block mode, in other words, when it has been instructed to use
When the Transfer Length is ZERO, no data will be transferred and the current position on the logical unit will not be changed.
If the READ command completes successfully in Fixed mode, the drive transfers (current Block Length) X (Transfer Length) bytes of data to the Initiator. 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 a 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 a CHECK CONDITION, if the requested Transfer Length is less than the actual block size recorded on the medium
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 and the Incorrect Length Indicator (ILI) bit and Valid bit will be set to one in the Sense Data. The Sense Key field is set to NO SENSE and the Information field is 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 Filemark, the drive will return a CHECK CONDITION status. the Filemark and Valid bits are set and the Sense Key field is set to NO SENSE. The Information field contains the residue count. The Additional Sense Code and Additional Sense Code Qualifier fields are set to Filemark Detected. Upon termination, the media will be logically positioned after the Filemark (EOM side).
If, however, the drive encounters a
If the drive detects EOD during the READ, the drive will return a CHECK CONDITION status and the Valid bit is set and the Sense Key field is set to BLANK CHECK. The Information field contains the residue count. The Additional Sense Code and Additional Sense Code Qualifier fields are set to EOD DETECTED. Upon termination,
SONY |
