A short introduction to Open Firmware_open firmware 1275-1994 specification pdf-优快云博客

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OpenFirmware是一种计算机固件系统的标准，定义了固件接口，并允许系统直接从PCI卡加载平台独立的驱动程序，提高兼容性。它最初由Sun Microsystems开发，并被Apple、IBM等公司采用。OpenFirmware基于Forth语言，提供了高效的硬件测试和调试能力。

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Open Firmware, or OpenBoot in Sun Microsystems parlance, is a standard defining the interfaces of a computer firmware system, formerly endorsed by the IEEE. It originated at Sun, and is used by Sun, Apple, IBM, and most other non-x86 PCI chipset vendors. Open Firmware allows the system to load platform-independent drivers directly from the PCI card, improving compatibility. The proposed Power Architecture Platform Reference will also be Open Firmware based.

Open Firmware may be accessed through its Forth language shell interface. It achieves essentially the same functionality as the later EFI standard initiated at Intel, with lower overhead.

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which was not reaffirmed by the Open Firmware Working Group (OFWG) since 1998 and has therefore been officially withdrawn by IEEE.

Several commercial implementations of Open Firmware have been released to the Open Source community in 2006, including Sun OpenBoot, Firmworks OpenFirmware and Codegen SmartFirmware. The source code is available from the OpenBIOS project. Sun's implementation is available under a BSD license.^[1]

Advantages

Because the Open Firmware Forth code is compiled into FCode (a bytecode) and not into the machine language of any particular computer architecture, Open Firmware code included in, say, an I/O card can be executed by any system that uses Open Firmware. In this way, an I/O card can provide boot-time diagnostics, configuration code, and device drivers that will be usable on any system running Open Firmware, allowing many of the same I/O cards to be used on Sun systems and Macintoshes.

Being based upon an interactive programming language, Open Firmware can be used to efficiently test and bring up new hardware.

Access

On Sun SPARC systems, the Open Firmware interface is displayed on the console terminal before the bootstrapping of the system software. 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. 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. While the system software is running, various Open Firmware settings can be read or written using the eeprom command.

On a PowerPC-based Macintosh, the Open Firmware interface can be accessed by pressing the keys Cmd-Option-O-F at startup.^[2] This functionality is generally only used by developers or troubleshooting I.T. personnel; for common users, the Mac OS X operating system provides a high level graphical user interface to change commonly used Open Firmware settings. For instance, it is possible to specify the boot disk or partition without directly using the Open Firmware interface. Other Open Firmware settings can be changed using the nvram command while the system software is running.

On Pegasos, the interface is accessed by pressing Esc at startup.

On IBM POWER systems, Open Firmware ("ok" prompt) can be accessed through the SMS Boot Menu. SMS Boot Menu can be accessed by pressing "1" or "F1" during the boot sequence, after hardware checking, and just before the OS boot.

On the OLPC XO-1 laptop, first get a developer key, which allows full access to the firmware. The key is readily accessible via the home page of the web browser. After you install the key, upon each power-on, you can interrupt the boot countdown with Esc (the upper left key) to get to the Forth ok prompt.