IPC/NETIPCFW-1A: User Documentation
DOC/NETIPCFW-E; V3.0
5 BIOS Extensions
5.1.
General Information
The BIOS provides a method for integrating add-on boards with on-board ROM code, called
BIOS extensions, into the system. During the POST, interrupt vectors are established for BIOS
calls. After the default vectors are in place, a scan for add-on board BIOS extensions occures.
At this point, an add-on board BIOS extension routine can gain control. The routine can
establish or intercept interrupt vectors to hook into the system.
Early in the POST the absolute addresses c0000h-c7fff are scanned in 2 kB blocks in search of
BIOS extensions that need to be initialized (for example, valid graphics controller VGA BIOS).
Later in the POST, the absolute addresses c8000h-effffh are scanned in 2 kB blocks in search
of devices with valid BIOS extensions.
Valid BIOS extensions are defined as follows:
Byte 0: 55h
Byte 1: aah
Byte 2:
a length indicator representing the number of 512-byte blocks (limit 7fh) in the BIOS
extension (length/512). A checksum tests the integrity of the BIOS extension code.
Each byte in the defined BIOS extension is summed modulo 100h. This sum must be
0 for the BIOS extension to be valid.
When POST identifies a valid BIOS extension, it executes a far call to byte 3 of the BIOS
extension (which should contain executable code). The device can now perform power-on
initialization. The BIOS extension should return to the POST by executing a far return.
If the BIOS extension diagnoses a self-test error, the following should be done before returning
to POST:
-
Set bit 4 of address hex 40:12 (POST status) to 1
-
Set the device number for the supported add-on board into register (AH)
-
Set a two-digit error code into register (AL)
If no self-test error is found, the BIOS extension should reset bit 4 of address hex 40:12 (POST
status) to 0 before returning.
5.2.
VGA BIOS Extension
All standard NETIPC boards include an onboard VGA graphics controller.
If enabled in the BIOS, the graphics controller requires a valid VGA BIOS extension to support
the basic video graphics functions defined for VGA. The VGA BIOS extension for the
NETIPC boards is part of the IPC/NETIPCFW-1A firmware. It is already programmed into the
onboard BIOS flash when delivered. If it is overwritten or deleted, it must be downloaded with
the Boot Loader Program using a prepared command file.
If the graphics controller is not needed, it may be disabled in the BIOS and the VGA BIOS
extension must be deleted in the onboard BIOS flash using the Boot Loader Program with the
command VGADEL. This overwrites the VGA BIOS extension code with all ffh’s.
Disabling the graphics controller will save some power and improve overall system
performance.
Actually different VGA BIOS extensions exist for the NETIPC products. To enable correct
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