Building an assembler

Question

I need to build an assembler for a CPU architecture that I\'ve built. The architecture is similar to MIPS, but this is of no importance.

I started using C#, although

Answer 1

If you are to write an assembler that just works, and spits out a hex file to be loaded on a microcontroller, it can be simple and easy. Part of my ciforth library is a full Pentium assembler to add inline definitions, of about 150 lines. There is an assembler for the 8080 of a couple dozen lines.

The principle is explained http://home.hccnet.nl/a.w.m.van.der.horst/postitfixup.html . It amounts to applying the blackboard design pattern to the problem. You start with laying down the instruction, leaving holes for any and all operands. Then you fill in the holes, when you encounter the parameters.
There is a strict separation between the generic tool and the instruction set.

In case the assembler you need is just for yourself, and there are no requirements than usability (not a homework assignment), you can have an example implementation in http://home.hccnet.nl/a.w.m.van.der.horst/forthassembler.html. If you dislike Forth, there is also an example implementation in Perl. If the Pentium instruction set is too much too chew, then still you must be able to understand the principle and the generic part. You're advised to have a look at the asi8080.frt file first. This is 389 WOC (Words Of Code, not Lines Of Code). An experienced Forther familiar with the instruction set can crank out an assembler like that in an evening. The Pentium is a bitch.