Editing Open Firmware (section)

== Features ==

Open Firmware defines a standard way to describe the hardware configuration of a system, called the ''[[device tree]]''.<ref name="Mauro" /> This helps the operating system to better understand the configuration of the host computer, relying less on user configuration and hardware polling. For example, Open Firmware is essential for reliably identifying slave [[I2C|I<sup>2</sup>C]] devices like temperature sensors for [[hardware monitoring]],<ref name="sensors-mmath" />{{rp|§5.1|q=5.1. Open Firmware and I<sup>2</sup>C}} whereas the alternative solution of performing a blind probe of the [[I2C|I<sup>2</sup>C]] bus, as has to be done by software like [[lm_sensors]] on generic hardware, is known to result in serious hardware issues under certain circumstances.{{r|sensors-mmath|p=§5.2|q=5.2. I<sup>2</sup>C bus scan through i2c_scan.c}}

Open Firmware Forth Code may be compiled into FCode, a [[bytecode]] which is independent of [[instruction set architecture]]. A [[Peripheral Component Interconnect|PCI card]] may include a program, compiled to FCode, which runs on any Open Firmware system. In this way, it can provide boot-time [[diagnostic]]s, configuration code, and [[device driver]]s. FCode is also very compact, so that a disk driver may require only one or two kilobytes. Therefore, many of the same I/O cards can be used on Sun systems and Macintoshes that used Open Firmware. FCode implements [[Forth (programming language)|ANS Forth]] and a subset of the Open Firmware library.

Being based upon an interactive programming language, Open Firmware can be used to efficiently test and bring up new hardware. It allows drivers to be written and tested interactively. Operational video and mouse drivers are the only prerequisite for a graphical interface suitable for end-user diagnostics. Apple shipped such a diagnostic "operating system" in many Power Macintoshes. Sun also shipped an FCode-based diagnostic tool suite called OpenBoot Diagnostics (OBDiag) used by customer service support and hardware manufacturing teams<ref name="OBDiag" />