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A Method to Circumvent the BIOS Option ROM Size Limitations

IP.com Disclosure Number: IPCOM000014993D
Original Publication Date: 2002-Mar-14
Included in the Prior Art Database: 2003-Jun-20

Publishing Venue



This publication provides idea of this invention is to provide a minimum sized Adapter "Option ROM" that can be loaded by PC BIOS into system Memory. This minimum sized "Option ROM" would only provide a basic interface to code running on the adapter, which would have more resources available to provide more functionality than can be handled in the limited "Option ROM" environment that we have in today's PCs. The following picture illustrates a typical AT Style personal Computer emphasizing the CPU, Real Mode Memory, Busses and Adapter. The discussion that follows is concerned with the boot time initialization of the PC. When the PC is first turned on or reset, the first instructions that are executed are from the BIOS ROM. The BIOS is responsible for initializing the hardware facilities on the PC, loading the Operating System, and providing an interface between the Operating System and the hardware platform. During the initialization process, the BIOS will configure what is labelled as the "CPU Bus to Adapter Bus Bridge" in the diagram above and then query the Adapter Bus for any adapters. When the BIOS detects an adapter, it will determine whether the adapter contains an "Option ROM". The Option ROM contains object code which is provided by the adapter card vendor. This Option ROM serves to provide BIOS support for complex adapters such as video or disk controller adapters, that are too complex for the PCs BIOS to manage. One problem that exists in today's environment, is the limited amount of resources available to option ROM in the System BIOS environment. The limited amount of resources is particularly evident in the amount of real mode memory the option ROM is allowed to occupy. This can severely restrict the functionality of complex adapter designs in the pre-OS environment. To alleviate the problem of limited space in real system memory, provided that our adapter contains it's own embedded processor that is capable of communicating with the option BIOS executing in the main (x86) processor, we can limit the size of the option ROM to be just large enough to provide an API that would pass commands to the embedded processor on the adapter card. This places the resource and processing burden on the adapter processor rather than the main PC processor, who's resources are currently being consumed by the system bios. The adapter card would contain all the resources necessary to provide the functions that it wants, without being limited by the real mode environment presented by today's BIOS. 1