RadiSys EPC-5A, Hardware & Software Reference Manual

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Chapter 5: Theory of Operation
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5 5
Keyboard Controller
The R400EX contains an Intel 8042-compatible keyboard controller. The keyboard
controller is addressable at the standard PC-AT architecture I/O addresses of 60h and
64h. Keyboard interrupts are signaled on IRQ1.
ROM and ROM Shadowing
The EPC-5A contains a 28F004-B*-T Flash Boot Block. The Flash device is mapped
into the top of the processor’s 32-bit address space. The Flash device contains the PC
BIOS, some peripheral BIOS code, and user extensions.
For best possible performance, the BIOS initialization software copies the ROM
contents into DRAM (called shadowing) at addresses 0F0000-0FFFFF. The BIOS
also searches for the existence of a video adapter containing a video BIOS (e.g., an
EXM-13A). If a video BIOS is found, it is copied into the 0Cxxxx area of DRAM.
After copying into these areas, the BIOS write-protects them. Subsequent writes to
these areas complete successfully but do not alter the data.
Embedded Shadow
The EPC-5A supports several different boot methods and operating systems. In order
to boot from VME or flash, it is necessary to first load and execute a BIOS extension.
The FBD has an unused 96KB region in main block #3 that lies between the end of
the PicoFlash extension and start of the System BIOS that can be used for BIOS
extension storage. In order to use this area for BIOS extensions, it is necessary to first
program the image into the FBD (using REFLASH.EXE) and then, at run time, copy
the BIOS extension from the FBD into DRAM, and have the System BIOS scan that
region for BIOS extensions. Multiple BIOS extensions can be programmed into the
user block of the FBD. Setup items allow the user to select up to 3 BIOS extensions
in the FBD and load them into DRAM between C8000h through DFFFFh.
Bootable Device Precedence
There are several bootable devices for the EPC-5A. Depending on the configuration,
either the EXM-2A, VME, SCSI or IDE can be the boot device. This section
documents the order in which these devices are installed in the boot chain. BIOS
extensions supersede IDE as a bootable device.