Read Buffer Command (3Ch) - Maxtor ATLAS 10K IV User Manual

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. The data format and field
descriptions are shown in Table 5-125 and Table 5-126 respectively.
Table 5-125
Bit
7
Byte
0
1
2
3 - 5
6 - 8
9
READ BUFFER Command-Data Format
6 5 4
Operation Code (3Ch)
Reserved
Buffer ID
Buffer Offset
Allocation Length
Control
SCSI Description
3 2 1
Mode
Maxtor Atlas 10K IV
0
5-91