Quantum 1200 Series DAT Autochanger Guía de usuario descargar pdf (Pagina 229)

SDLT 600 SCSI Interface Guide Chapter 4: SCSI Commands

81-81200-02 REV A01 January 2005 4-187

4.17.3 Data Mode (02h)

In this mode, the DATA IN phase contains only buffer data. This mode can be used to check the

diagnostic read buffer to see if an unexpected error has occurred.

4.17.4 Descriptor Mode (03h)

In this mode, the drive returns a maximum of 4 bytes of READ BUFFER descriptor information. The

drive returns the descriptor information for the buffer specified by the Buffer ID. In this mode, the

drive does not reject the invalid Buffer IDs with a CHECK CONDITION status, but returns all zeros in

the READ BUFFER descriptor. The Offset Boundary is 3, indicating that buffer offsets should be

integral multiples of 8.

Figure 4-97. READ BUFFER Descriptor — Data Format

4.17.5 Read Data from Echo Buffer (0Ah)

In this mode the drive transfers data to the application client from the Echo Buffer. The Echo Buffer

transfers the same data as when the WRITE BUFFER command with the mode field set to Echo Buffer

was issued. The Buffer ID and Buffer Offset fields are ignored in this mode.

The READ BUFFER command returns the same number of bytes of data as the drive received in the

previous Echo Buffer mode WRITE BUFFER command from the same initiator. If a previous Echo

Buffer mode WRITE BUFFER command did not complete successfully, the drive terminates the Echo

Buffer mode READ BUFFER command with a CHECK CONDITION status, with Sense Key set to

ILLEGAL REQUEST, and the Additional Sense Code set to COMMAND SEQUENCE ERROR. If

the data in the Echo Buffer has been overwritten by another initiator, the drive terminates the command

with a CHECK CONDITION status, with Sense Key set to ABORTED COMMAND and the

Additional Sense Code set to ECHO BUFFER OVERWRITTEN.

Bit

Byte

7 6 5 4 3 2 1 0

0 Offset Boundaries (0Ch)

1 – 3

(MSB)

Buffer Capacity

(LSB)

1 2 ... 224 225 226 227 228 229 230 231 232 233 234 ... 293 294

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Quantum 1200 Series DAT Autochanger Guía de usuario Pagina 229