The following is the text-only version of the Forth & FCode proposal.


Open Firmware
Recommended Practice:

Forth source & FCode image support
Version 1.0
(NOTE:  this is an UNAPPROVED DRAFT)


Published by the Open Firmware Working Group

This document is a voluntary-use recommended practice of the Open Firmware
Working Group. The Open Firmware Working Group is an ad hoc committee
composed of individuals interested in Open Firmware as defined by IEEE
1275-1994, related standards, and their application to various computer
systems.
The Open Firmware Working Group is involved both in IEEE sanctioned
standards activities, whose final results are published by IEEE, and in
informal recommendations such as this, which are published on the Internet
at:
        http://playground.sun.com/pub/1275
Membership in the Open Firmware Working Group is open to all interested
parties. The working group meets at regular intervals at various locations.
For more information send email to:
        p1275-wg@risc.sps.mot.com

Revision History
1.  Introduction
Various platform bindings (e.g., PReP) specify particular load image
formats that are supported by that platform's Open Firmware
implementations.  This recommended practice adds support for both Forth
source code and FCode images.  These formats are to be supported on all
platforms.
While different image formats are supported on a platform by platform
basis(e.g., ELF), two formats are inherently defined by the base IEEE Std
1275-1994 document.  These are Forth source  (as defined by Open Firmware)
and FCode.
The intent of this recommended practice is that all Open Firmware
implementations shall recognize these two formats and deal with them as
defined within this document.
2.  Forth source
A valid Forth source load image shall be recognized (by init-program) when
the first two bytes of the load image have the binary values 0x5C,0x20,
which are the (ASCII) character values for '\',' '  (reverse-slash, space).
This character sequence is the standard way of introducing a comment into
Forth source.
Such a load image is then assumed to contain lines of Forth source text,
each of which is terminated by a line-end (a carriage-return (0x0D)
optionally preceded or followed by a line-feed (0x0A)).
init-program, upon recognizing a Forth source image, shall set the state of
Open Firmware such that a subsequent execution of go will cause the loaded
Forth source image to be processed as if the lines of text were being
entered, line by line, as console input to the Open Firmware User
Interface.  This interpretation of Forth source text shall be guarded by
catch;  if the evaluation causes an error, Open Firmware shall enter the
User Interface.
3.  FCode image
A valid FCode load image shall be recognized (by init-program) when the
first two bytes of the load image have the binary values 0xF1,0x08 (the
first two bytes of a start1 FCode header) and having a valid checksum.  The
checksum is computed using the length field of the presumed FCode heaader
and is compared to the checksum field of that header.  If the image passes
these tests, then it is assumed to be a valid FCode image.
Upon detecting an FCode image, init-program shall set the state of Open
Firmware such that a subsequent execution of go will cause the FCode image
to be evaluated (as with byte-load).  This evaluation shall be guarded by
catch;  it the FCode evaluation causes an error, Open Firmware shall enter
the User Interface.