Specifications

14 AMD Geode™ GeodeROM Functional Specification
Overview
32087C
■ Legacy USB
— GeodeROM can be configured to support legacy USB, thereby allowing the use of a USB keyboard and mouse
before a driver is loaded by the operating system. Associated with this functionality is a “virtual keyboard controller”
module, allowing for a standard keyboard BIOS look and feel, in the absence of a keyboard controller.
■ USB Floppy Boot Support:
— Supports booting USB floppy drives in systems without a standard floppy drive.
■ Legacy BIOS Entry Points
— GeodeROM provides the legacy BIOS function entry points for use by legacy software as a compatibility feature.
■ PCI ‘_32_’ Services Directory Table
— Provides a ‘_32_’ bit service directory that provides the operating system information regarding the location of the 32-
bit PCI BIOS API. Some operating systems use the information in this table to determine the presence and location of
32-bit, flat-mode PCI BIOS services. The ‘_32_’ bit service directory is described in revisions 2.1 and newer of the
PCI BIOS Specification.
■ PCI BIOS 32-Bit Protected Mode API
— Provides a flat-mode, 32-bit protected mode interface to those PCI bus access functions defined in revisions 2.1 and
newer of the PCI BIOS Specification.
■ Power-On Splash Screen (supports .BMP format)
— Contains special sequences of ROM-based code for displaying OEM-supplied splash screens during the power-on
sequence, rather than the traditional text-mode DRAM count and similar displays. The current GeodeROM implemen-
tation supports 320x200, 640x480, 800x600, 1024x768, and 1280x1024 .BMP file formats.
■ Power-On Time Option ROM Invocation/Initialization
— Shadows and invokes any option ROMs that adhere to the format specified in documents such as “The IBM PS/2
Model 60 Technical Reference Manual.” Such option ROMs contain a special “55h/AAh” header, size byte, and initial-
ization entry point. GeodeROM searches for and invokes any valid ROMs that reside on 2 KB boundaries in region
C800:0h-DF80:0h. Option ROMs can be found on ISA cards, PCI devices, or be embedded in the GeodeROM image.
■ Power-On Time PCI Enumeration/Configuration
— Automatically detects, initializes, and configures PCI 2.1 compliant devices that appear in PCI configuration space
following a power-on sequence. GeodeROM contains a resource allocation module that assigns I/O, address space,
and IRQ resources to PCI devices, and ensures the resources assigned to the devices are conflict free. GeodeROM
also programs the steering and edge/level values of IRQs assigned to PCI devices during the power-on sequence.
■ Protected Mode Reset
— GeodeROM supports the 286-style reset typically used for returning the microprocessor from protected mode to real
mode. Functions 05h and 0Ah are currently supported. The caller resets the microprocessor by writing the function
value into CMOS location 0Fh and resetting the system.
■ Compression/Decompression for BIOS Modules (Plus Compression Utility)
— Provides developers the capability of storing code and data modules in compressed form within the system Flash or
EEPROM device. Compressed modules contain a header that identifies the type, size, target decompression
segment, compression method, and other information used to build or manipulate the compressed module. During a
power-on or reset sequence, and following DRAM bank configuration, GeodeROM decompresses such modules into
system shadow RAM space. Compression usage has the advantage of conserving build time ROM device space,
enabling developers to include significantly more functionality in a ROM device than would be possible without the
use of compression. A DOS utility is provided that compresses source ROM modules and supplies these modules
with the correct header information.
■ SDRAM Bank Sizing/Geode Processor DRAM Controller Initialization
— Determines the amount of memory installed in the system’s SDRAM banks, configures the processor’s SDRAM
controller with the appropriate row/column information, and initializes the SDRAM timings. If the SDRAM modules
support SPD (Serial Presence Detection) EEPROMs, special GeodeROM code queries the SPD EEPROMs via a
standard ACCESS.bus interface and may optimize the SDRAM timings based on the reported capabilities of a partic-
ular SDRAM module.