SCSI Pass-Through Programmer's Guide

Recent Enhancements
1. User notification of Bus Resets
Without this enhancement a bus reset (a.k.a powerfail reset, power-on reset) will result in
device configuration settings (SCSI MODE SELECT) made by an application program being
lost silently.
This enhancement enables the different SCSI DMs (SCSI Tape DM, SCSI Tape2 DM, SCSI
Disc DM and SCSI DISC ARRAY DM) to ‘remember’ a bus reset and return a device_reset
status back to the application program.
The following are some details regarding this enhancement:
• Each DM ‘remembers’ a bus reset when it happens. During the subsequent I/O
processing, the I/O request is not forwarded to the lower I/O levels. The DM returns a
device_reset status (0x800) to the application program. The next I/O request will be
processed as usual.
• It is recommended that programmers always begin with a ‘TUR’ (Test Unit Ready)
command so that any stale device reset status is flushed out. (Programming note:
MPE/iX drivers typically perform the following commands: IDENTIFY, TUR, TUR,
TUR, IDENTIFY to clear all possible bad status and verify a device is available).
• When there are multiple accessors (independent programs, threads, forked
children/parent) of a particular DM, it should be noted that only the first accessor
after a bus reset will return a device_reset status. An I/O that is in progress during the
bus reset will also return a device_reset status.
• On receipt of a device_reset, the program should re-issue any MODE SELECT
commands to re-set any device operating configuration.
This enhancement is available via patch MPENX03A for MPE/iX release C.75.00.
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