73 lines
2.8 KiB
Markdown
73 lines
2.8 KiB
Markdown
avremu: An AVR Emulator written in pure LaTeX
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[5]
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LaTeX is known as a typesetting system. But the underlying TeX system
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is a powerful macro processor. In fact, TeX is a Turing-complete
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programming language. TeX can compute anything, that is
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computable. Computeability is a concept from theoretical computer
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science. After visiting a theoretical CS course, you will know that
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there are things that cannot be solved by a machine. Never. Look out
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for the halting problem. So, Turing-complete does not say "It's a
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proper programming language", but more "someone can write a proper
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interpreter for any programming language in it, theoretically".
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So back to TeX. To be honest, TeX is a horrible language to code
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in. After writing my master thesis in LaTex, after crafting every
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graphic within with TiKz[1] and pgfplots[2], and after writing my
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first LaTeX package[3], I can honestly say: TeX is the Quasimodo of
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all widely used programming languages. If you can avoid it, avoid it.
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But if you are forced to use it, you can abstract from TeX, since it
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is a "proper" programming language.
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Let's say we want to program our document in C on Top of Tex. Then
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there would be the need to interpret the C semantic. Basically we
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would have to write a compiler for C in TeX. Not a very promising
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future, if you start this. But, we can use a normal C compiler to
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compile the C code to some simple platform. Like AVR[4]. Since I have
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other things to do than writing an AVR Emulator in TeX, here it is!
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The newest source can be found at https://gitlab.brokenpipe.de/stettberger/avremu
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## You are writing an CPU emulator in TeX, the TYPESETTING system? ##
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Yep.
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## What Microcontroller is emulated? ##
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I aimed for an ATmega8. The AVR platform is an 8 Bit Processor with 16
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Bit memory addresses. The hardware version is shipped with 1 KByte of
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RAM and 8 Kbyte Flash memory, but of course, the emulated processor
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can handle more memory.
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## Are you insane? ##
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Not that anybody knows of.
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## Are all OP codes implemented? ##
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Unfortunately not. I'm still missing 5 opcodes (MULS, MULSU, FMUL,
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FMULS, FMULSU), but until now I did not encounter a C file, the
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AVR-GCC emits these opcodes. The fractional multiply opcodes are also
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somewhat arcane.
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## Is it fast? ##
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Ok, you are asking me, whether a CPU simulator written in TeX, that
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simulates an 8-Bit microcontroller is fast? Propably not. On my
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notebook I could achieve 2.5 KHz, so this is a factor 10000 slower
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than the actual hardware with the highest supported clock rate.
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-----
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[1] http://www.ctan.org/pkg/pgf
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[2] http://pgfplots.sourceforge.net/
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[3] http://www.ctan.org/pkg/dataref
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[4] http://en.wikipedia.org/wiki/Atmel_AVR
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[5] A Mandelbrot Set. The image took 44 hours to be calculated
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