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mkasm

An assembler for the PDP-8 using modified PAL syntax.

Features

mkasm supports PAL-III syntax with a few additional useful features.

Memory Reference Instructions

All standard PDP-8 Memory Reference instructions are implemented. Reference specifiers I and Z are available for specifying indirect and page addressing, respectively.

OPR Micro-Instructions

Currently only group 1 and 2 operate instructions are supported.

IOT Instructions

Standard IOT instructions for a teletype are built in.

Additional Features

mkasm includes some features not found in the PAL assemblers. These have to be enabled with the -D flag.

Single Quotes - Single quotes can be used to get ASCII codes of characters. This can be useful for storing character values into memory. The trailing quote is optional.
Example: DASH, '-'

Double Quotes - Double quotes can be used to store C-style ASCII strings. Each character in the string is stored in consecutive memory locations followed by a NUL (0).
Example: HELLO, "Hello, World!\n"

Usage

Compile programs written in PAL Assembly into several different formats. The most basic usage is mkasm example.pa which producs a Pobj binary example.po.

Current supported output formats are:

  • Pobj: Human readable format produced by pdpnasm. Each instruction is encoded as 4 ASCII digits that represent a 12-bit octal number. Addresses are prefixed with 17.

  • RIM: Format used on the OG PDP-8. This format was used to bootstrap the PDP-8 as a simple RIM loader could be keyed in manually. This binary format encodes each instruction into 4 bytes. The first two bytes are the address followed by two bytes containing the instruction to store at the address. The first byte in the address always has bit 7 set.

  • URL: Format used for mkweb.

Usage: mkasm [options] <src_file> [out_file]

Options:
  -D    Support additional PAL-D syntax
  -dump
        Dump program listing to stdout
  -err-ctx int
        Lines of context surrounding errors
  -help
        Print this message and exit
  -list
        Generate program listing file
  -pobj
        Output in PObject (.po) format
  -rim
        Output in RIM format
  -size
        Print program size information
  -url
        Output in URL format
  -url-base string
        Base URL to use for URL format.

Build

Building this project requires go, this can be downloaded online.

To build the assembler, first clone this repository:

git clone https://github.com/Rex--/mkasm.git

Then build the project:

cd mkasm
go build .

This should produce the binary mkasm in the directory.

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Copyright (c) 2024 Rex McKinnon
This software is available for free under the permissive University of Illinois/NCSA Open Source License. See the LICENSE file for full details.