This functionality is generally only used by developers or troubleshooting I.T. Also, early versions (before the PowerBook 3400) connect Open Firmware's input and output to the Modem port by default. Intel-based Macintoshes do not use Open Firmware they use Extensible Firmware Interface. On a PowerPC-based Macintosh, the Open Firmware interface can be accessed by pressing the keys ⌘ Cmd+ ⌥ Option+ O+ F at startup ( ⊞ Win+ Alt+ O+ F if using standard PC USB keyboard). While the system software is running, various Open Firmware settings can be read or written using the eeprom command. If no keyboard is connected, then the first serial line on the system is usually used as the console and Open Firmware is re-entered by sending a "Break" on the serial line. If a keyboard is connected, the main video display will be used as the console terminal and Open Firmware can be re-entered at any time by pressing Stop+ A ( L1+ A) on the keyboard. On Sun SPARC systems, the Open Firmware interface is displayed on the console terminal before the bootstrapping of the system software. Sun also shipped an FCode-based diagnostic tool suite called OpenBoot Diagnostics (OBDiag) used by customer service support and hardware manufacturing teams Access Apple shipped such a diagnostic "operating system" in many Power Macintoshes. Operational video and mouse drivers are the only prerequisite for a graphical interface suitable for end-user diagnostics. It allows drivers to be written and tested interactively. FCode implements ANS Forth and a subset of the Open Firmware library.īeing based upon an interactive programming language, Open Firmware can be used to efficiently test and bring up new hardware. Therefore, many of the same I/O cards can be used on Sun systems and Macintoshes that used Open Firmware. FCode is also very compact, so that a disk driver may require only one or two kilobytes. In this way, it can provide boot-time diagnostics, configuration code, and device drivers. A PCI card may include a program, compiled to FCode, which runs on any Open Firmware system. Open Firmware Forth Code may be compiled into FCode, a bytecode which is independent of instruction set architecture. For example, Open Firmware is essential for reliably identifying slave I 2C devices like temperature sensors for hardware monitoring, : §5.1 whereas the alternative solution of performing a blind probe of the I 2C 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. This helps the operating system to better understand the configuration of the host computer, relying less on user configuration and hardware polling. Open Firmware defines a standard way to describe the hardware configuration of a system, called the device tree. Sun's implementation is available under a BSD license. The source code is available from the OpenBIOS project. Several commercial implementations of Open Firmware have been released to the Open Source community in 2006, including Sun OpenBoot, Firmworks OpenFirmware and Codegen SmartFirmware. Open Firmware is described by IEEE standard IEEE 1275-1994, which was not reaffirmed by the Open Firmware Working Group (OFWG) since 1998 and has therefore been officially withdrawn by IEEE in May 2005. Open Firmware may be accessed through its command line interface, which uses the Forth programming language. Open Firmware allows the system to load platform-independent drivers directly from a PCI device, improving compatibility. It originated at Sun Microsystems, where it was known as OpenBoot, and has been used by vendors including Sun, Apple, IBM and ARM. ![]() Open Firmware is a standard defining the interfaces of a computer firmware system, formerly endorsed by the Institute of Electrical and Electronics Engineers (IEEE).
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