NFP09 - An IEEE 754 floating point library for the MC6809

NFP09 is a floating poing library for the MC6809 microprocessor, based on the original Motorola MC6839 floating point firmware for MC6809 microprocessor, updated to build with the asm6809 assembler.

This work began as a fork of fp09, which is copy of the original code written in 1980 and released by Motorola in 1988. The original code is preserved, without any modification, in the src/ directory, as well as Rich Kottke's documentation in the doc/ directory.

All of the modified source code lives in the newsrc/ directory. In that directory, you'll find copies of the original source code, modified for the new assembler, a Makefile, and a master source file called nfp09.s, which is responsible for including all of the other source files in the correct order. nfp09.s is the file that is built by asm6809 to produce the binary image.

nfp09.s exists primarily because asm6809 does not support multi-object linking. Another upshot of this is that all symbols end up in the same namespace. To avoid polluting the namespace, I've made extensive use of asm6809's local label feature. Alas, there were a few instances where I needed to tweak conflicting symbol names or comment out duplicate-but-equal equates.

Not all of the original source files have been converted. I converted only those that were required to build a binary image (I kept adding source files until I no longer had unresolved symbols). Note that this will NOT build a fully-compaible 6839 ROM image; specifically, I have left off the trailing file that rounds it to 8K and includes the CRC ("endit.sa"). If someone is interested in this functionality (i.e. linkability into OS-9 using the standard mechanisms), I'm definitely open to it, but I didn't tackle it initially because it's not required for my target application (which is to embed this library inside another ROM image).

Files that have been converted

check.sa
comp.sa
compare.sa
dispat.sa
equates.sa
fads.sa
fmuldv.sa
frmsqt.sa
frnbak.sa
getput.sa
ins.sa
intflt.sa
mvabsneg.sa
notrap.sa
outs.sa
procs.sa
rndexep.sa
util.sa

While converting the source files, I also made an effort to beautify the source code. There is now a consistent indentation style, with an attempt to keep everything as uniform as possible. Because of the limitations of asm6809's macro language, most of the macros used in the original code were not used. In particular, the control flow macros (IF-ELSE-ENDIF and WHILE-ENDWH) were expanded by-hand and sometimes re-structured to produce more efficient code. There are still opportunities for optimization in this area. The goal, of course, is not to make a binary that is identical to the original 6839, but rather to implement the same functionality in a way that is cycle- and space-efficient.

Major to-do items

I have found some for-sure bugs and some maybe bugs. They're tagged with XXXJRT and I need to file Issues for them.
I need to go through the warts.sa file and determine if issues need to be filed for those items as well.

Minor to-do items

Go back and remove some of the commented-out IF-ELSE-ENDIF comments. I originally kept them, but stopped including them as I converted more files beause it just made things harder to read.

Integration and documentation

Kottke's historical documentation is useful, but no longer completely accurate for NFP09. I have used it as the basis for the interface documentation that can be found in nfp09-abi.s. That file also contains all of the equates necessary to use NFP09 in a way that won't pollute your application's own symbol namespace with a bunch useless junk.

Testing