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The user interface operates as an interactive Forth environment, with necessary omissions and additions as appropriate to Open Firmware. The interface should be used to develop and debug the Forth source code that will eventually be converted into FCode and stored in a PCI card's expansion ROM. To create FCode, which is a tokenized representation of the Forth source, you must use an FCode tokenizer. Apple provides the standalone tokenizer in the PCI driver development kit (DDK). Special tokenizer words automatically generate a ROM image with the correct signatures and formats for a PCI card expansion ROM with FCode.
The Open Firmware interface interprets common Forth words as well as user defined words. The following sections list some of the common Forth commands that are available for Open Firmware driver development and debugging. The Forth language interpreter and Open Firmware implementation details are well defined in the documentation listed in Other Publications. This chapter provides only a brief introduction the features available in the Open Firmware environment.
While testing your forth code in the Open Firmware interface, you may get stuck in a situation that causes an infinite loop. You can get out of this situation by shutting down Open Firmware with a press of the Power key on the keyboard.