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General Requirements

Any Open Firmware driver must be stored in a PCI card's expansion ROM so that the Macintosh firmware can load and run the driver prior to the invocation of the disk-based operating system. Open Firmware drivers are written in FCode. For further information about FCode, see Writing FCode Programs for PCI. This book is listed in Other Publications.

Other general requirements for Open Firmware drivers include the following:

• They must be able to acquire any software resources they need from the PCI card's expansion ROM or from the Macintosh firmware. For example, a display card must be able to access a font in the expansion ROM if it is required to write characters on the screen during startup.
• The card hardware may not address system space below 1 MB. In Power Macintosh computers, PCI cards that request space below 1 MB in a reg property will not receive a corresponding assigned-addresses entry.
• PCI expansion cards and their drivers should avoid hard address decoding, as discussed in Hard Decoding Device Address Space.