http://mcosre.sourceforge.net/docs/open_firmware/of_overview.html
12/5/2007
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Firmware is the ROM-based software that controls a computer
between the time it is turned on and the time the primary operating
system takes control of the machine. Firmware's responsibilities
include testing and initializing the hardware, determining
the hardware configuration, loading (or booting) the operating system,
and providing interactive debugging facilities in case of faulty
hardware or software. Open Firmware is processor and system independent boot firmware. Open Firmware is the non-proprietary name of firmware complying with the IEEE Std 1275-1994: Standard for Boot (Initialization, Configuration) Firmware, Core Requirements and Practices. Among Open Firmware's many features, it provides a machine independent device interface, which can be used to boot plug-in cards without providing OS-specific and/or machine dependent binary programs on the plug-in card. This feature enables plug-in card manufacturers to easily support several independent computer architectures without needing to supply different firmware for each one. Open Firmware is based on Sun Microsystem's OpenBoot 2.x implementations and complies with ANS (ANSI) Forth. OpenBoot 3.x, shipping on Sun's 64-bit UltraSparc based systems, complies with the Open Firmware standard. Apple Computer's line of PCI bus-based Power Macintosh(tm) desktop systems are shipping with Open Firmware.
Open Firmware's primary task is to control the machine from the time power is applied until the primary operating system has been loaded and has taken control of the machine.
In typical operation, Open Firmware performs the following sequence of
operations, in the order given:
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