Quantum 10K II - Manual (Page 206)

SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–139
5.22 READ BUFFER Command (3Ch)
The READ BUFFER command is used in conjunction with the WRITE BUFFER
command. It allows the initiator to gain access to the data storage areas within the
drive's controller. In particular, these two commands are used to check the integrity
of the buffer-initiator data path, independent of the media, typically for fault
isolation in the event of a failure. In addition, these commands can be used to verify
the caching policies of the drive controller or other kinds of diagnostic and
verification work.
Both the READ BUFFER and the WRITE BUFFER commands have a buffer ID and
a buffer offset data field defined in their Control Descriptor Block. In the Combined
Header and Data Mode, if both are set to 0, reference is made to a single 512-byte
buffer set aside in the drive 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 (3Ch)
1 Reserved Mode
2 Buffer ID
3 - 5 Buffer Offset
6 - 8 Allocation Length
9 Control
Figure 5–58 READ BUFFER Command — Data Format