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Six
Registered: Apr 2002
Posts: 322 |
JAM instruction
Does anyone have a description of what happens internally in the CPU to make the JAM instructions lock up? I'm curious if anyone has looked into exactly WHY they behave like they do and thought it might be an interesting topic to research, but not sure where to start. |
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Mixer
Registered: Apr 2008
Posts: 460 |
Could this be of some use to your research?
http://visual6502.org/JSSim/index.html |
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Ninja
Registered: Jan 2002
Posts: 418 |
IIRC some C= Hacking magazine had an explanation. They are all on the web... |
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MagerValp
Registered: Dec 2001
Posts: 1082 |
They figured it out with Visual6502 and Michael Steil has a good explanation on his blog:
http://www.pagetable.com/?p=39
TL;DR: the instruction decoder is a state machine, and some illegals get it to a state where it never finishes the current instruction. |
