"The Ultimate M68K Cheat Sheet" is a document heavily influenced by MarkeyJester's work, who used a real Genesis to determine cycle counts for all M68K instructions with every source and destination operand possible.
My ultimate cheat sheet attempts to do the same, but ultra-compacts the information into as few tables as possible (31 tables to be exact, covering 9 pages) and incorporates notes from the famous "68000.pdf" (author unknown) floating around, making the beginner's difficult journey to mastering the M68K a whole lot easier.
By studying this document, you also learn what combinations of operands are possible for each instruction, and the cycle cost/availability as a byte, a word, or a long word operation. (For instance, "–/8/8" means that a byte version is not available, but a word and a longword is available at 8 cycles.)
To download my "ultimate" M68K cheat sheet, click here.
I've also taking a similar approach to programming the Genesis's VDP, by documenting different registers and techniques (such as DMA operations) into small, compact tables that take no more than 4 pages.
To download my "ultimate" Genesis VDP cheat sheet, click here.
Also, for practicing M68K assembly, I have been rewriting/improving existing decompression code found in Sonic the Hedgehog 1 (and apparently used by many other games such as Golden Axe), whose source is freely available.
To download my improved Nemesis decompression code for use with Sonic 1: click here.
To download my improved Kosinski decompression code for use with Sonic 1: click here.
To download my improved Enigma decompression code for use with Sonic 1: click here