User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Read Buffer (3Ch)
Quantum DX-Series Software Interface Guide 235
Table 184 READ
BUFFER Command
Descriptor Block -
Field Descriptions
The host should first send a READ BUFFER command, in Descriptor
mode, to determine the size of the buffer being returned. In response to
the READ BUFFER command, the tape system returns four bytes of data,
three of which contain the size of the buffer. The host can then use this
data to establish the Buffer Offset/Allocation Length fields of the CDB.
Field Name Description
Mode The tape drive supports the following values within this field. If any non-
supported value is set, the drive terminates the command with a CHECK
CONDITION status, ILLEGAL REQUEST sense key set.
ModeDescription
000b Combined Header and Data
010b Data
011b Descriptor
Buffer ID Must be 0, 1, or 2.
Buffer 0: This buffer is intended to be used in conjunction with the WRITE
BUFFER command to provide a diagnostic capability for testing the SCSI bus
and/or hardware integrity.
Buffer 1: Choosing Buffer 1 results in the tape system transferring the contents
of SCSI RAM and EEPROM over the SCSI bus. For DLT7000 tape systems, a
total of 264K is transferred (4K for RAM).
Buffer 2: Choosing Buffer 2 results in the tape system transferring the contents
of cache RAM over the SCSI bus. For DLT7000 tape systems, a total of either 4
or 8 MB is transferred.
Buffer Offset Supported if Buffer ID is 2. The Buffer Offset field allows the host to specify
where the start of the data is within the buffer.
Allocation
Length
This field specifies the maximum number of bytes that the initiator has
allocated for returning data. The host uses this field to limit the size of data
transfers to its own internal buffer size.