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5-94 Maxtor Atlas 10K V
5.20 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 5-123 and Table 5-124 respectively.
Table 5-123 READ BUFFER Command-Data Format
Bit
Byte
7654321 0
0 Operation Code (3Ch)
1 Reserved Mode
2 Buffer ID
3 - 5 Buffer Offset
6 - 8 Allocation Length
9 Control