Quantum 10K II - Manual (Page 288)

SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–221
5.49 WRITE BUFFER Command (3Bh)
The WRITE BUFFER and the READ BUFFER commands allow the initiator to gain
access to the data storage areas within the drive controller. These commands are
used to check the integrity of the buffer-initiator data path independent of the
storage medium, typically for fault isolation. The commands can be used to verify the
caching policies of the controller or other kinds of debug work. In addition, the
WRITE BUFFER command supports controller microcode downloads.
Both the READ BUFFER and WRITE BUFFER commands have a
Buffer ID and a
Buffer Offset data field defined in their Command Descriptor Block. In combined
Header and Data Mode, if both are set to 0, reference is made to a single, 512-byte
buffer set aside in the controller's data memory, independent of cache. This allows an
initiator to verify the data path from the controller's data memory to the initiator
without affecting the drive's internal data caches.
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (3Bh)
1 Reserved Mode
2 Buffer ID
3 - 5 Buffer Offset
6 - 8 Parameter List Length
9 Control
Figure 5–109 WRITE BUFFER Command Descriptor Block — Data Format