This emulator was written from scratch originally with the help alone of the Wikipedia (CHIP-8), and later on with Cowgod's Manual.
The emulator is written in a single main.s assembly file and graphics are
rendered to screen through the help of SDL, which
you need if you want to compile. The emulator was written for the x86-64
platform under Linux (important to note that the data is stored in memory
as little-endian, primarily to swap two bytes, as the CHIP-8 uses big-endian).
The file is heavily commented, so you should be able to follow along even if you have little experience with assembly, and I hope it can teach people something.
As for a quick overview on the code, the machine registers and program
memory are just "variables" defined on the .data segment.
There are methods to set/unset the pressed state of the keys, to draw the screen buffer, and to beep while the sound timer is not zero.
The emulateprogram method reads instructions one by one and parses the
operation by jumping to the right position (e.g. 0xFx29 jumps to F),
further performing more comparisons if more fine-tuning is necessary to
determine the operation to execute. There's a delay to mimic the 60Hz of
the machine, and events (e.g. key events) are polled right proceeding.
The main method reads the ROM into memory and sets up SDL, exiting on error.
I do not own any of the ROMs available in the roms/ folder, which were
picked up from other several websites hosting them, neither I do own the
text written by Thomas P. Greene CHIP8-TECHNICAL.txt.
An amazing reference on calling conventions (and more) for the x86-64 platform is available at http://wiki.osdev.org/System_V_ABI#x86-64.
You can find most of the used SDL methods on https://wiki.libsdl.org/.