ADPATCH can patch games to directly support the OPL2LPT. After patching, configure the game for an Adlib sound card (in case this isn't auto-detected).

Caveats:

• Patching can break sound card support (including support for non-Adlib cards).
• Patched games might only work on the computer where the patch was done. This is because the patch hardcodes the parallel port I/O address, which I believe might vary from computer to computer.

Pros compared to the ADLiPT TSR:

• No need for 386 CPU
• No Adlib emulation slowdown
• Can work with protected mode games

Cons:

• Patches need to be written for each game by hand

• Sierra
  • Games using the "SCI" engine. Patch ADL.DRV.
• id Software
  • The Commander Keen series
  • Wolfenstein 3D
  • DOOM (v1.9 tested)
  • DOOM II
• Softdisk
  • Keen Dreams
  • Dangerous Dave's Risky Rescue
  • Dave Does Nutz
• Apogee
  • Bio Menace

Games not listed almost certainly will not work (sorry). Patches welcome :)

To compile a DOS executable using OpenWatcom, use the build.sh script. To compile with GCC, use the buildunix.sh script.

You'll also need Python 3, the NASM assembler and the Ragel state machine compiler.

The patches are stored in YAML files in the patterns/ directory. Each file can have multiple patches, I try to keep related patches together. Generally each target needs two patches, one for the Adlib detection routine and one for the actual Adlib I/O.

Each patch consists of a search pattern and a replacement code fragment.

The search pattern is specified as an assembly fragment, but there are certain special keywords that can be used.

ANYBYTE, ANYWORD, ANYDWORD can be used as a wildcard for an arbitrary 1/2/4 byte value. For example:

mov dx, word ptr [ANYWORD]
out dx, al

In this pattern, the address of the variable is not important and might differ in different builds of the game. So it's best to accept anything.

BEGIN/ALT/END mark alternative code sequences. For example:

BEGIN
  mov dx, 0x389
ALT
  inc dx
END

This is useful to match slight variations in a single pattern.

BEGIN/REPEAT marks possible repetition. For example:

BEGIN
  in al, dx
REPEAT

The fragment must appear at least once.

BEGIN/OPTION marks a fragment that might or might not appear.

BEGIN
  nop
OPTION

ANYBYTE/ANYWORD won't work for relative offsets. So instead of call ANYWORD, you'll have to write db 0xE8, ANYBYTE, ANYBYTE. Same for short jumps.

Surprisingly often x86 instructions have multiple encodings. For example, mov ax,bx might be encoded as 89 D8 or as 8B C3. If NASM picks the wrong encoding, you'll have to spell out the bytes explicitly.

The implementation is a gross hack.

The replacement code is an ordinary assembly fragment. The keyword PORT can be used once to get the parallel port I/O address.

ADPATCH ships with a few standard replacements that can be %included:

• standard.s: the standard OPL2LPT code. Expects the OPL2 register in AL and the data in AH.
• standard32.s: same, as 32-bit code.
• compact.s: a slower but smaller version. Will pop register and data (separately) from the stack.

If the replacement code is shorter than the matched fragment, it will be padded with NOPs.