Reference Guide

Chapter 4 SCSI Commands
READ BUFFER Command (3Ch)
DLT-S4 Interface Reference Guide 266
Retrieving Diagnostic Data 4 The host should first send a READ BUFFER command in Descriptor mode
(Mode 3) to determine the size of the buffer being returned. In response to
the
READ BUFFER command, the drive returns 4 bytes of data, 3 of which
contain the size of the buffer. Note that this may take a while to complete
(possibly as much as 1 minute). The host uses this data to establish the
Buffer Offset and Allocation Length fields of the CDB. Once the host
knows the size of the buffer, the host sends a Mode 2
READ BUFFER
command to transfer the data.
Read Data from the Saved Buffer (A1h) 4
The A1h buffer (the saved buffer) contains information saved from an
event that caused the drive to unexpectedly reset. Use Mode 3 to test for
event data. The event data is not actually generated with this first
READ
BUFFER
command—instead, the size of the data is returned.
Read Data from the Live Buffer (A2h) 4
The A2h buffer (the live buffer) contains the latest information about the
current state of the tape drive. The buffer is populated each time a
READ
BUFFER
command using Mode 3 with the A2h buffer ID is received by
the drive. The information in this buffer is most useful when an error
occurred that did not cause an unexpected reset of the drive; for example,
a Hard Read Error (HRE) or a Hard Write Error (HWE).
The buffer contains actual event data. Note that retrieving this
information overwrites any other saved event information, so it is best to
check the size of the Saved Buffer first to check if there is any useful
information available (do this with a Mode 3
READ BUFFER command,
described in Descriptor Mode (03h)
on page 267).
Note: If the length of this buffer is 0, an unexpected reset event has
not occurred.