Quantum DLT 8000 Product Manual page 310

SCSI Commands
READ BUFFER Command (3Ch) (continued)
Table 5–74 READ BUFFER Command Descriptor Block — Field Descriptions
Field Name
Mode
Buffer ID
Buffer Offset
Allocation Length
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. Once the size of the buffer is known, Mode 2 (Data Only, see
Section 5.16.2) can be used to transfer the data across the SCSI Bus.
5-166
Description
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.
Mode Description
000b Combined Header and Data (see 5.16.1)
010b Data (see 5.16.2)
011b Descriptor (see 5.16.3)
Must be 0, 1, or 2.
Buffer 0: This 1100 KB 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 controlled scratchpad RAM and EEPROM over
the SCSI bus. For DLT 8000 tape systems, a total of 264K is
transferred (256K for RAM, 8K for EEPROM).
Buffer 2: Choosing Buffer 2 results in the tape system transferring the
contents of data cache RAM over the SCSI bus. For DLT
8000 tape systems, a total of 8 MB is transferred.
The Buffer Offset field allows the host to specify where the start of
the data is within the buffer.
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.
Quantum DLT 8000 Tape System