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