Specifications

74 AMD Geode™ GeodeROM Functional Specification
PCI Support
32087C
Power-On PCI Device Configuration Support
During its power-on sequence, GeodeROM assigns IRQs, I/O, and memory ranges to PCI adapters requesting such sys-
tem resources. GeodeROM scans the PCI bus in ascending order. I/O and memory ranges are assigned in a “top-down”
fashion, starting at FFFFh and FFE00000h, respectively.
Assignment of PCI IRQ Channels
The same IRQ channel is assigned to all PCI devices. It is expected that the operating system can share IRQ channels
between devices. In a basic implementation, INTA# is routed to IRQ11. Similarly, IRQ11 is programmed to be level sensitive
in the Geode South Bridge’s ELCR (Edge/Level Configuration register). In cases where the operating system does not sup-
port IRQ sharing, GeodeROM can be built to steer PCI interrupt channels other than INTA# to different PC/AT IRQ chan-
nels.
Assignment of PCI I/O Ranges
PCI devices are assigned I/O ranges starting above the ISA limit of 0FFFh. Such a strategy ensures there are no resource
conflicts between PCI and legacy devices. GeodeROM contains a simple resource allocation module that assigns I/O
ranges in descending order as they are required by installed PCI devices.
Assignment of PCI Address Space Ranges
PCI devices are assigned address ranges starting above the ISA limit of 0FFFFFh. Such a strategy ensures there are no
resource conflicts between PCI and legacy devices. Additionally, GeodeROM ensures there are no conflicts between those
address ranges assigned to PCI devices and the ranges used by SMM software-related functions. GeodeROM contains a
simple resource allocation module that assigns address ranges in descending order as required by installed PCI devices.
Support for PCI Option ROM
GeodeROM contains functionality to detect, shadow and initialize PCI option ROMs. As required by the PCI specification,
PCI option ROMs are left writable during their initialization sequence to allow such ROMs to modify their own code space.
Support for PCI Bridges
GeodeROM does not contain PCI bridge support except to avoid corrupting a PCI bridge device.