Intel IA-32 - Manual (Page 409)

Vol. 3A 9-35
PROCESSOR MANAGEMENT AND INITIALIZATION
9.11 MICROCODE UPDATE FACILITIES
The Pentium 4, Intel Xeon, and P6 family processors have the capability to correct errata by
loading an Intel-supplied data block into the processor. The data block is called a microcode
update. This section describes the mechanisms the BIOS needs to provide in order to use this
feature during system initialization. It also describes a specification that permits the incorpora-
tion of future updates into a system BIOS.
Intel considers the release of a microcode update for a silicon revision to be the equivalent of a
processor stepping and completes a full-stepping level validation for releases of microcode
updates.
A microcode update is used to correct errata in the processor. The BIOS, which has an update
loader, is responsible for loading the update on processors during system initialization
(Figure 9-7). There are two steps to this process: the first is to incorporate the necessary update
data blocks into the BIOS; the second is to load update data blocks into the processor.
Table 9-5. Relationship Between BLD Item and ASM Source File
Item ASM386 and Startup.A58 BLD386 Controls
and BLD file Effect
Bootstrap public startup
startup: bootstrap
start(startup) Near jump at
0FFFFFFF0H to start.
GDT location public GDT_EPROM
GDT_EPROM TABLE_REG
<> TABLE
GDT(location =
GDT_EPROM) The location of the
GDT will be
programmed into the
GDT_EPROM location.
IDT location public IDT_EPROM
IDT_EPROM TABLE_REG <> TABLE
IDT(location = IDT_EPROM The location of the IDT
will be programmed
into the IDT_EPROM
location.
RAM start RAM_START equ 400H memory (reserve =
(0..3FFFH)) RAM_START is used
as the ram destination
for moving the tables. It
must be excluded from
the application's
segment area.
Location of the
application
TSS in the
GDT TSS_INDEX EQU 10 TABLE GDT(
ENTRY = (10:
PROTECTED_MODE_
TASK)) Put the descriptor of
the application TSS in
GDT entry 10.
EPROM size
and location size and location of the
initialization code SEGMENT startup.code
(base = 0FFFF0000H)
...memory (RANGE(
ROM_AREA = ROM(x..y)) Initialization code size
must be less than 64K
and resides at upper
most 64K of the 4-
GByte memory space.