Open Firmware

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Open Firmware is the hardware-independent firmware (computer software which loads the operating system) that the XO-1 runs.

It was developed by Mitch Bradley at Sun Microsystems, and used in post-NuBus PowerPC-based Apple Macintosh computers (though it has been dropped with Apple's transition to Intel processors), Sun Microsystems SPARC based workstations and servers, IBM POWER systems, and PegasosPPC systems, among others. On those computers, Open Firmware fulfills the same tasks as BIOS does on PC computers.

It is accessed by a user by a FORTH-based shell interface. FORTH is a powerful high level language.

For example Fedora and Debian use the YaBoot BootLoader for OpenFirmware.

Source Code

The source code for the firmware used in the XO-1 is available in the OpenFirmware subversion repository. To find the software used in a given OLPC release, look on the Firmware page to find the release, then look on the release page for the "svn" revision number. E.g. for OLPC Firmware q2d07 the revision number is 775. You can browse the Subversion repository and view or download the code (actual repository is at svn://openbios.org/openfirmware/).

Replacing BIOS in the XO - a historical overview -

Inside was a development BIOS and bootloader used for a very short time until we were able to bootstrap our own. At that point, we moved to LinuxBIOS for both low-level hardware initializer and bootloader, which was less than ideal and somewhat unwieldy. In a surprise move, SUNW then opened up their parts of the OFW/OBP code under a BSD license, which allowed Mitch Bradley (at that point working for us) to open up his own parts -- that of his company, FirmWorks -- and let us have an acceptably-licensed OpenFirmware we can use as a fancy and compact bootloader. LinuxBIOS did low-level hardware initialization, transfered control to OFW, which then also acting as boot loader to load Linux OS.

Since the "c" series of firmware releases starting on April 6, 2007, LinuxBIOS has not been present at all. The low-level init is now done with a few lines of assembly language code and a big table of register values.

Removing LinuxBIOS was what made it possible to get the startup time down to a couple of seconds, and to do the firmware part of resume in a few milliseconds.

source Questions on LinuxBIOS and OpenFirmware

Activating Open Firmware on an XO

There are two ways to get to OFW on an XO, at boot time and from Sugar.

  • At boot time, press and hold the checkmark game-control button (right on old XOs with unmarked game keys). Release when instructed and press the Escape key (top left on the XO keyboard, with a white X in a black circle. In a few seconds, the FORTH ok prompt appears.
  • In the Terminal activity, execute the command
echo y > /proc/sysrq-trigger

See FORTH for a brief introduction to the FORTH programming language, which Open Firmware is written in, plus links to other resources.

Be careful with OFW. You can seriously mess up or brick your XO with it. You might want to experiment in gForth first.

See also

External links

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