view docs/manual/c13.html @ 416:b4d0eafc5bfe

Fix code generation error in gcc6809 It turned out that under some circumstances, the gcc optimizer would select an instruction sequence that had the sense of a branch inverted. It seems this was due to a particular instruction pattern included in the machine description not being quite right with respect to how the condition codes were tracked. Removing that instruction pattern seems to fix things (subtraction with the arguments reversed). gcc seems to be smart enough to figure out how to reorganize code to work without this reversed sense subtraction and then do the right thing.
author William Astle <lost@l-w.ca>
date Thu, 24 Mar 2016 20:07:20 -0600
parents b30091890d62
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>Chapter 1. Introduction</H1
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>The LW tool chain provides utilities for building binaries for MC6809 and
HD6309 CPUs. The tool chain includes a cross-assembler and a cross-linker
which support several styles of output.</P
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>For a long time, I have had an interest in creating an operating system for
the Coco3. I finally started working on that project around the beginning of
2006. I had a number of assemblers I could choose from. Eventually, I settled
on one and started tinkering. After a while, I realized that assembler was not
going to be sufficient due to lack of macros and issues with forward references.
Then I tried another which handled forward references correctly but still did
not support macros. I looked around at other assemblers and they all lacked
one feature or another that I really wanted for creating my operating system.</P
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>The solution seemed clear at that point. I am a fair programmer so I figured
I could write an assembler that would do everything I wanted an assembler to
do. Thus the LWASM probject was born. After more than two years of on and off
work, version 1.0 of LWASM was released in October of 2008.</P
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>As the aforementioned operating system project progressed further, it became
clear that while assembling the whole project through a single file was doable,
it was not practical. When I found myself playing some fancy games with macros
in a bid to simulate sections, I realized I needed a means of assembling
source files separately and linking them later. This spawned a major development
effort to add an object file support to LWASM. It also spawned the LWLINK
project to provide a means to actually link the files.</P
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