Browse Prior Art Database

Method to Improve Initial Microcode Loading for Personal Computers

IP.com Disclosure Number: IPCOM000113422D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 110K

Publishing Venue

IBM

Related People

Deckys, D: AUTHOR [+6]

Abstract

Described is an implementation to improve operational procedures during Initial Microcode Load (IML) of Personal Computers (PCs).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method to Improve Initial Microcode Loading for Personal Computers

      Described is an implementation to improve operational
procedures during Initial Microcode Load (IML) of Personal Computers
(PCs).

      In prior art, the increased functionality of PCs has resulted
in the IML recurring during certain paths of the Power-On Self Test
(POST) operation.  On these paths, the user could not start the
operating system if the IML occurred from a diskette.  The concept
described herein provides an operating procedure that improves IML
sequencing.

      When a PC is powered ON, POST is executed from an
Electronically Programmable Read Only Memory (EPROM) in the certain
segments until the media becomes available.  The POST uses the IML
process to load the remaining POST/BIOS code that is on the media and
not in the EPROM.  The IML can occur from either a diskette, or from
a fixed disk.  If the fixed disk becomes unavailable, such as when
power supply cables become defective, or there is no fixed disk in
the system, IML must occur from a diskette.  This can present a
problem, if the reference diskette does not contain the IML code.

      In certain PCs, the entire IML fits into the required segments,
128 Kb total, requiring an increase in the amount of code needed for
POST hardware testing, thereby exceeding 128 Kb size of 2 segments.
Therefore, changes are required in portions of the IML that are read
into memory in blocks of 16 Kb code, called overlays.  This loads
greater than 128 Kb into a 128 Kb area by loading in a 16 Kb portion
of the IML as needed and allows the correct portion of POST code to
be executed during the proper test.  Once the final overlay is loaded
into memory, its execution reads the master boot record and transfers
control to it, thereby booting the system.

      In the situation when the hardfile is unavailable, the system
must load the IML from the reference diskette and the reference
diskette is booted displaying the main menu.  If the option "Start
the Operation" is selected, or if the main menu is exited with the F3
function key, a problem can be encountered.  On certain PCs, the
entire IML image is in memory, so no IML needs to occur.  At this
point, the reference diskette can be removed and replaced by a
bootable diskette.  POST completes its testing, loads the master boot
record from the bootable diskette, and the operating system starts.
In this case, the entire IML does not remain in memory and a se
cond IML process is needed, requiring the reference diskette to
remain in the drive.  This prevents the replacement of the reference
diskette by a bootable diskette until the I...