Quantum DLTtape DLT1, Interface Manual

Page: 164 / 182

Chapter 4: SCSI Commands
4-122 July 2004 81-81276-01 Rev A01
4.26.1 Header and Data Mode
A 4-byte header consisting entirely of reserved bytes precedes the data to be transferred. The tape drive
discards this header (does not store it into the buffer). The buffer offset field must be 0 for this mode.
4.26.2 Write Data Mode
Similar to mode 000b, except no header is in the data passed to the target. The Buffer Offset must be 0.
The target detects potential buffer overruns and rejects the command.
4.26.3 Download Microcode Mode
Using buffer offsets, the host can download the firmware image into the target’s buffer in pieces. These
commands do not cause the new image to become active; a Download and Save mode WRITE
BUFFER command must be issued.
The tape drive must be empty to allow downloading an image. This is to safeguard against accidentally
starting a firmware update. If a data cartridge is loaded when all or part of a firmware image has been
downloaded, the tape drive rejects any other WRITE BUFFER with Download Microcode mode.
Overlapping or nonconsecutive downloading of the image data is not supported. The firmware image
must be downloaded in integral multiples of 8KB.
Any error on a WRITE BUFFER command causes the tape drive to discard any downloaded image
data and requires restarting the download from the beginning.
Buffer ID For all modes, only a Buffer ID of 0 is supported. If the Buffer ID field is non-
zero, the target rejects the command. The target detects and rejects commands that
would overrun the buffer.
Buffer Offset Buffer offsets are allowed to be non-zero. However, only integral multiples are
valid. The offset boundary in the descriptor mode page of the READ BUFFER
command reports the allowed integral multiple for buffer offset values.
Table 4-71.
WRITE BUFFER (3Bh) Command Descriptor Block — Field Descriptions
Field Name Description