A work-in-progress attempt at reverse engineering a bitwise perfect compilable source of NHL 94 for Sega Genesis. Requires original ROM file to build.

Built on the work that McMarkis (https://github.com/Mhopkinsinc/NHLHockey) did to get the NHL 92 source compiling, and my work to make the code bitwise perfect to the retail version. Also references chaos' disassembly work of NHL 92-94 (https://github.com/Chaos81/nhl94-disassembly).

Code Disassembly: 0 / 309152 bytes completed = 0% complete

Asset Identification: I think this the majority of the remaining 323 kb, and I want to say this is about 90% done. I think the main thing will be to double check the code as I find the references to the files in the disassembly to fine tune the start/ends of files. I'm not sure if I've identified the exact starts of every file, or just where the useful data begins.

• Retail version is bitwise perfect with retail ROM. Rev A Dev build is bitwise perfect with Rev A Dev build included with original release.
• Documentation of all File Formats used within the game
• Script which changes opcodes to match the custom compiler EA used to build the game
• Disassembled Retail Validation Check code included via checksum env variable
• Env vars allows build of Retail version (includes validation code), Rev A "retail" version (includes validation code) or Rev A Dev version (no validation code)
• Script to generate CRC16 Checksum used in ROM Header & CRC32 Checksum used in Validation code
• EA Logo code is disassembled and buildable
• Sound Driver code is disassembled and buildable
• Script to extract assets from retail rom (Graphics, PCM audio, FM audio, z80 snd driver)
• Requires retail ROM

1. Install node from https://nodejs.org/en/download if it isn't already installed on your machine

2. In the NHLPA93Genesis folder, run npm i to install node_modules

3. Copy the NHLPA Hockey 93 Sega Genesis ROM file into the NHLPA93Genesis folder

4. Run node .\extractAssets93.js <nhlpa93RomFileName> to extract assets from the NHLPA Hockey 93 ROM file into the Extracted folder

5. Run npm run build:logo to build EALogo93.bin (modified_EALogo93.bin is the opcode corrected version)

6. Run npm run build:sound to build Hockey93.snd (modified_Hockey93.snd is the opcode corrected version)

7. You have the choice of building 3 versions:

   • For the Retail ROM, run npm run build:retail -- this includes the retail checksum validation check (modified_nhlpa93.bin is the opcode corrected version)

   • For the Rev A ROM, run npm run build:reva -- this includes the retail checksum validation check (modified_nhlpa93.bin is the opcode corrected version)

   • For developing your own version, run npm run build:dev -- this uses Rev A flags and does not include the retail checksum validation check (modified_nhlpa93.bin is the opcode corrected version)

You need to build using build:dev to avoid the checksum validation. By default, this builds the Rev A version of the code. If for whatever reason, you do want to enforce checksum validation on your build, you need to use the generateChecksum.js script. Also, you need to do 2 passes of the script & updating the checksums to end up with the correct checksum for both CRC16 and CRC32. The game will not start if checksum validation is enabled and the checksum is incorrect.

TBD.

TBD.

TBD

TBD

Documentation for the NHLPA93 .JIM and .JZIP file format and tools to import/export to/from .JIM/.JZIP format lives here: https://github.com/abdulahmad/EA-NHL-Tools/tree/main/JIM-Tools

Documentation for the NHLPA93 .ANIM file format and tool to export from .ANIM format lives here: https://github.com/abdulahmad/EA-NHL-Tools/tree/main/ANIM94-To-BMP

.pal files use standard Genesis CRAM format for palette. Each color is 2 bytes in Genesis format (0000BBB0GGG0RRR0, where BBB=Blue bits, GGG=Green bits, RRR=Red bits).

Note: This section has not been updated for NHLPA93 yet.

Pointer table at $1035C (35 entries, longwords relative to p_music_vblank). Maps SFX IDs (0-34) to handlers (e.g., $0 = handle_sfx_siren). Some duplicates/share code (e.g., IDs 30-34 all point to handle_sfx_id_30).

Handlers (e.g., handle_sfx_puckwall1) load YM2612 params or init channels via Sound_InitSFXChannel. Many write direct to YM2612 (e.g., Sound_WriteYM2612) for freq/volume, or chain to others (e.g., puckwall3 chains to pass).

Extracted .bin files (e.g., sfx_siren_cmdstream_ch0.bin at $FF74). Byte streams parsed in Sound_Process_SFXChannels: $80 (set instrument), $81/$82 (delay/alt delay), $83 (freq sweep: counter, base freq, increment), $84 (stop), $85 (loop). Frequency normalized to YM2612 range ($000-$7FF).

Extracted signed 8-bit PCM .bin files (e.g., sfx_puckwall1_pcm.bin 0x11C3E-0x12A58). Streamed via DAC. Some shared/partial (e.g., sfx_puckbody_pcm overlaps FM patches at $12A58). Sample rates ~8-11kHz based on counters.

Loaded via $80 command. Params: 4 operators (mul/dt/tl/rs/ar/dr/sr/rr/ssg-eg), alg/fb, stereo. 25+ defined; some hardcoded in handlers (e.g., fm_instrument_patch_sfx_id_3 at $12DE2 overlaps PCM).

At $1017A (96 bytes): YM2612 freq low bytes for notes (C0-B7, incl. sharps). E.g., C0=$02, C#0=$03. Used in process_note_frequency with octave shifts.

At $101DA (96 bytes): Freq high/octave bits. E.g., C0=$84, C1=$AA. Combined with freq table for full 11-bit YM2612 freq.

At $1023A (4 long ptrs to envelopes). Signed vibrato/detune patterns ($00 neutral, positive up, negative down; $84 loop). E.g., Envelope0: subtle oscillate (0,+1,+1,0,-1,-2,-1,0,loop). Applied in check_envelope for pitch/volume modulation.

At $10294 (5 entries, 26 bytes each): Num FM/PSG channels (word), 6 long ptrs to channel data (rel to p_music_vblank). E.g., Title ($0506, ch0-5 ptrs).

Channel offsets (e.g., fmtune_song0_ch0 at $10568): Words pointing to sequences (e.g., $11A3 = seq0). Up to 6 channels per track.

Sequences (fmtune_seq0 at $1061E+): Byte streams for notes/rests ($00-$5F note/rest, $60 rest), commands ($80+ as in SFX but music-specific: $80 instr, $81 mod, $83 sustain, $84 loop, $85 stop, $86 env, $87 clear env, $88 pitch, $89 flag, $8A skip, $8B SFX). Durations $8C-$9F (multiplied by tempo).

Binary at $116A6-$11C3D (extracted as z80_snd_drv.bin). Loaded via Sound_LoadZ80Program. Disassembled (IDA Pro):

• Entry: Z80_SoundDriver ($116A6) sets stack ($1FFF), IM1, jumps to MainLoop ($116D6).
• MainLoop: Checks flags (FLAG_CONTROL $02A4). Processes DAC ($2A reg), FM channels (6x, regs $30-$8C via ProcessFMChannels $11775), PSG. Busy-waits for YM writes.
• Channels: Pointers at $0073. Flags at $00B0. Processes per-channel (key on/off $28, freq $A0/$A4, vol $4C).
• DAC/PSG: DAC enable ($2B reg). PSG via shared RAM ($00BE-$00C3).
• Writes: WriteYM2612 ($118DF) / WriteYM2612Part2 ($118EB) with delays (pop hl for timing).
• Instruments: Patched to YM regs (e.g., $30+ for operators).

• PCM Overlaps: Some FM patches overlap PCM (e.g., $10820 in fm_instrument_patch_sfx_31). Modding may corrupt audio due to hardcoded address
• Checksum Sensitivity: Builds require exact extracts for bitwise match; minor ROM diffs break validation.
• Z80 Sound Driver: There is an .lst file in the sound folder of the z80 sound driver disassembly, but I haven't gone through the effort of making it part of the build-- the z80 code extracted from the retail rom is used for the build.

• Custom Music: Edit fmtune_pointer_table / sequences. Add notes via freq tables; test envelopes for vibrato.
• New SFX: Add to sfx_pointer_table, create handler (init channels, YM writes), cmdstream (.bin), PCM if needed.
• Testing: Build dev for no checksum lock. Monitor shared RAM ($FFFFFE40+) for channel states.