Getting started

This repository holds a commented disassembly of Demonia for the MSX (Microids, 1986, cassette). Everything here comes out of the binary and can be generated from it again.

What you need

• Python 3 (no third-party packages)
• pasmo, to reassemble
• z80dasm, used only for the mnemonics
• the tape, which this repository does not distribute

The tape goes in the root, named demonia.cas. It is exactly 58,334 bytes:

sha256  69031ee25099df0703332ca74a64b52e6dd9909e4cfded4c3699be153adc5fc9

The Makefile asks for it by that sha256 and warns if it does not match.

The test that matters

make verify

This reassembles the thirteen listings with pasmo and compares the result against the original .cas, byte for byte. Here that takes one step more than a cartridge would: first every listing is checked on its own, and then the chunks are glued back together in the order the tape carries them, with their sentinels, their headers and their padding. If it prints OK, the disassembly has invented nothing: it is the same tape written differently.

Everything else you can run

make            # the whole cycle: extract, trace, list, verify
make listados   # regenerates the thirteen src/demonia_*.asm
make sanity     # the checks reassembly does NOT cover
make test       # the tests
make densidad   # how many comments each routine carries
make sobra      # the accounting for what the game carries and never uses
make imagenes   # redraws the PNGs in docs/imagenes from the tape
make web        # regenerates this site

make sanity is the one that watches for what a correct reassembly can hide: data being read as code. The bytes come out the same either way, because they do not change; the only thing that changes is what we say about them.

The tests run without the tape

The nineteen tests in tests/ need neither the tape nor make: they read the thirteen published listings, which is where every byte lives — the defb rows carry the data with its address, and the instructions carry theirs in the generated comment.

That was deliberate. A test that skips itself when a file is missing is a place to hide a check that never actually runs; and besides, what gets published is the listing, so the listing is what needs watching. If someone hand-edits a defb, the tests notice. No rigour is lost, because make verify already proves that assembling those listings gives the tape back exactly.

Where to go next

• The game — what Demonia is and how it is put together
• The tape — thirteen blocks, three files sharing one name and 26 KB hidden underneath the ROM
• The code — the memory map, the tables and the stowaway
• Findings — what turned up when we took it apart
• Open questions — what could not be closed