Browse Prior Art Database

Search Initial Microcode Load Execution during PS/2 Post

IP.com Disclosure Number: IPCOM000113876D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 182K

Publishing Venue

IBM

Related People

Cronk, D: AUTHOR [+6]

Abstract

Disclosed is a Search IML feature by which the microcode in an EPROM module searches all SCSI hardfiles for the latest Initial Microcode Load (IML) image appropriate for the machine type being initialized. When this image is retrieved, the reference partition is also retrieved and updated on the disk from which the IML image is retrieved.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 35% of the total text.

Search Initial Microcode Load Execution during PS/2 Post

      Disclosed is a Search IML feature by which the microcode in
an EPROM module searches all SCSI hardfiles for the latest Initial
Microcode Load (IML) image appropriate for the machine type being
initialized.  When this image is retrieved, the reference partition
is also retrieved and updated on the disk from which the IML image is
retrieved.

      The Power-On Self Test (POST) and BIOS code in IBM PS/2* Models
90 and 95 resides in the E000 and F000 segments of memory.  Upon
power-on, POST and BIOS execute out of the EPROM module until the
media becomes available.  Then, in a process known as Initial
Microcode Load (IML), an image is loaded from the media to shadow RAM
in the E000 and F000 segments.

      Without the Search IML feature, the IML image must reside on a
fixed disk with a SCSI Physical Unit Number (PUN) of 6, connected to
a SCSI adapter card with a PUN of 7.  The Reference Partition, using
a version of DOS as an operating system, accesses the disk by means
of interrupt 13h, reading and writing only to the hardfile designated
as 80h.  Thus, it is not possible to connect two systems having the
IML feature on a single SCSI bus without adding at least one
additional SCSI adapter to one of the systems.

      On the other hand, a system having the Search IML feature can
be twin tailed on a SCSI bus with another system.  This capability is
achieved by leaving the SCSI PUNs of the hardfile and adapter card in
the other system unchanged, as the PUNs of the hardfile and adapter
in the system having the feature are changed to values other than 6
and 7.  Furthermore, the Search IML feature allows a user to
configure a single system with redundant IML images to increase
system availability.  If an appropriate IML image is not located on a
hardfile, the search routine looks for a compatible image on any
removable disks that are attached to the SCSI bus.  If there are no
removable disks, or if a suitable IML image is still not located,
fixed optical drives and then removable optical drives are then
searched.  When it is necessary to retrieve the Reference Partition
from a disk, the search routine swaps the SCSI table so that the
drive with the IML image appears as the first drive, 80h, to the
reference programs, which assume that the System Partition is on
drive 80h.

      Fig. 1 is a diagram showing two systems with the same IML image
sharing a single SCSI bus.  When the systems are powered on, the POST
tests residing in an EPROM initializes video and SCSI circuits, and
the first megabyte of memory.  Then, the Search IML feature reads the
last 5 sectors of each hardfile, starting with the highest PUN, 5.
On a hardfile having an IML image, the IML boot record is in the last
sectors of the file, so this data is checked for a valid signature.
The IML boot record may take up three or five sectors, depending on
the system.  If a boot record is found in...