a80

a80 is an assembler written in D for the Intel 8080 (and, by extension, the Zilog Z80) CPU.

a80 is developed on OpenBSD but should work on any system that D targets.

a80 is not an exact clone of any pre-existing CP/M assember, nor does it want to be. The differences will be explained in this document.

a80 also is quite conscious about its design practice and implementation. It is written to be the subject of a series of blog posts in which we attempt to demystify the building of programming tools, and as such very intentionally does not use some very obvious data structures. And it may make some seemingly peculiar design choices. My goal is to have written a real assembler for a real CPU that you can still purchase today (in the form of the Z80) that true beginners can come to understand.

After the blog series, if we want to turn this into a clone of an existing CP/M assembler, I'm all for it.

Bug reports are welcome at any time.

Usage

a80 file.asm

The output will be file.com.

Syntax

A line of assembly takes the following form:

[label:] [op [arg1[, arg2]]] [; comment]

Example assembly programs can be found in hello.asm, fib.asm, and mul.asm.

a80 only understands Intel 8080 opcodes.

The CP/M EQU directive is supported however you cannot use other labels as a value nor can you use expressions.

All op and arg must be lowercase, though labels may include capital letters.

Numbers

Numbers may be in decimal or hex.

Hex numbers must end with an h. If a hex number begins with a-f, it must be prefixed with 0. This is not too dissimilar compared to other CP/M assemblers.

Strings

The DB pseudo-op is available. Strings can be written within single quotes. The multi-comma syntax is not available.

Expression parser

There is none. That is to keep things simple.

The equ pseudo-op does allow for $ and very simple $+number expressions only. No spaces in expressions. Valid expression operands are +, -, *, /, and %.

License

ISC license. See LICENSE for more information.