SCSI Pass-Through Programmer's Guide

1. Some SCSI hardware implementations include a controller that can monitor the status
of devices in the enclosure and provide this information through SCSI commands. In
practice, this information can be used to detect problem conditions like high
temperatures or simply allow one to set an LED on a device to help pin-point it in a
data center. SPT would enable programmers to obtain this information despite the
fact that MPE/iX does not have a “SCSI Enclosure Controller Device Manager.”
2. Some currently supported devices provide features that MPE/iX is not aware of. For
instance, Ultrium Tapes allow a new type of File Indexing for faster searching of the
media. MPE/iX has no knowledge of these features. A third party back-up tool might
want to use SPT, instead of the MPE/iX File system, to be able to insert these media
indexing marks on their tapes.
History and some caveats
The underpinning routines of this SCSI Pass-Through (SPT) interface have been present in
MPE/iX since the 6.5 Release. In 6.5 the SPT interface was provided as an extension to
MPE’s POSIX interface for the exclusive use of the MPE/iX diagnostic tools
(CSTM.DIAG.SYS). As these routines were originally designed as a porting enabler for an
internal HP tool they may be a bit “rough around the edges”. Therefore while this document
describes a method of accessing these features of MPE, it may not describe every nuance and
option of the interfaces. A working program and code examples are provided such that an
experienced MPE/iX “C” programmer should be able to make use of what we have provided;
this is not a document for beginners. Given the power of the SPT interface one should
approach using it with the same caution, care, and thought given to MPE/iX Privilege Mode
programs.
WARNING: Sending SPT commands to a device in use by MPE or other applications may
result in data loss, data corruption and/or System Aborts. We do not recommend sending
SPT commands to Disks with MPE/iX volumes present nor should one access tapes devices
which are used for normal back-up or data logging purposes. Rule of thumb: Don’t do SPT
to tape or disk media you cannot recover, nor at a time you don’t wish to cause a system
outage.
We have tested, during this program or indirectly via the CSTM utilities, these interfaces
with most of HP’s Supported SCSI devices using 6, 10 and 12 Byte SCSI Commands. We
have not tested with any “unsupported devices” nor with 20 Byte SCSI Commands. This
interface is provided on an “as is” basis and no warrantee of usefulness or applicability
should be assumed or is implied by the existence of this document.
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