Browse Prior Art Database

Read-Only Memory Recovery in a System with Initial Microcode Load

IP.com Disclosure Number: IPCOM000111273D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 127K

Publishing Venue

IBM

Related People

Bealkowski, R: AUTHOR [+4]

Abstract

Disclosed is a method for enabling computer systems to load and execute a firmware image stored in ROM (Read-Only Memory), without depending on magnetic media. Using this method, systems without media (i.e., without a diskette drive and without a fixed disk), and systems displaying media errors which would otherwise halt the initialization process, can implement loadable firmware during an IML (Initial Microcode Load) cycle.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Read-Only Memory Recovery in a System with Initial Microcode Load

      Disclosed is a method for enabling computer systems to load and
execute a firmware image stored in ROM (Read-Only Memory), without
depending on magnetic media.  Using this method, systems without
media (i.e., without a diskette drive and without a fixed disk), and
systems displaying media errors which would otherwise halt the
initialization process, can implement loadable firmware during an IML
(Initial Microcode Load) cycle.

      The IML process allows a set of routines coded into ROM to load
a run-time firmware image from a media source, such as a diskette or
fixed disk, into a portion of RAM, called "Shadow-RAM," which is
memory mapped as the system firmware address space.  This dynamically
loaded image then becomes the firmware used in the remainder of
system operation.  This image includes portions of POST (Power-On
Self-Test) and BIOS (Basic Input/Output System) routines necessary
for the initialization and operation of the system.  With the IML
process, system initialization is divided into Stage 1, in which a
minimum set of routines is loaded from ROM, and Stage 2, in which an
image is copied from a media source into Shadow-RAM.  Stage 2 is
begun when enough routines have been provided to allow the copying of
the Stage 2 firmware image in this way.

      To facilitate the operation of systems without media, systems
with the IML feature are required to maintain a copy of a Stage 2
firmware image in local nonvolatile storage, such as ROM.

      As shown in the flow chart, the IML process includes a number
of checks to determine from which media---fixed disk, diskette, or

ROM---the Stage 2 firmware image is to be loaded.  After the IML
process is started in block 10, the process checks the validity of a
Stage 2 image in ROM in block 12.  As a result of this check, a ROM
VALID status is set in block 14, or a ROM INVALID status is set in
block 16.  This status information is subsequently used to determine
the flow of the IML process.

      Next, in block 20, a determination is made whether the system
has been placed in Diskette Priority Mode, to initially attempt to
load the Stage 2 image from a diskette.  If the system is in this
mode, a determination is made in block 22 of whether the system has a
diskette drive containing a valid Stage 2 image.  However, since the
IML feature is provided as a means for upgrading POST and BIOS
routines, it is important that the most recent image is loaded into
Shadow-RAM.  Therefore, in block 24, the date of the Stage 2 image on
the diskette is compared with the date of the Stage 2 image in ROM.
If the diskette image is not older than the ROM image, the diskette
image is loaded into Shadow-RAM in block 26, and the initialization
process is continued with Stage 2 in block 28.

      If the system is not in Diskette Priority Mode, as determined
in block 20, if the no valid diskette image is foun...