Darkman

01 · Music

The music plays before a level and never during one

The title pages and the briefing text play three tunes, and a fourth is in the game and never starts. Jonathan Dunn is credited with the sound. The player below runs the game's own driver on the kit's 6502 simulator, calls it once a frame, and plays what the driver writes to the sound chip.

The driver is the title copy at $A0C8, in the bytes of level 1's file from $817C to $93AB, and the player calls $A242 once a frame, 50.12 times a second on a PAL machine. The page supplies only the player, the note display, and the filter, which starts as a model of a 6581 chip; its cutoff curve is one chip's, and real chips differ. Each tune was checked against the same calls on the kit's 6502 simulator (test_music.js): 520,674 writes to the sound chip over 12,000 frames of each tune, in order, with no difference.

Level 1's title code starts a tune by calling $A164 with X set to six times the tune number. The title pages play tune 3, or tune 1 when the new-high-score flag at $110F is set. Tune 0 starts at $0F70 whenever no voice is playing while the briefing text is typed. Nothing in the game loads X with 12, so tune 2 never starts, and it is the only tune that ends: the other three loop. Once play begins, nothing calls the tune player again.

Tune	Started at	Track lists, voices 1 to 3	Plays	Wave programs	Patterns
0	`$0F70`, with the briefing text	`$ADAD` `$ADA0` `$ADB2`	Loops every 1,920 frames (38.3 s)	0 and 1	0, 1, 6
1	`$0AC1`, when the new-high-score flag is set	`$AF5A` `$AF93` `$AFA6`	An opening of 1,344 frames (26.8 s), then loops every 960 (19.2 s)	4 to 6	2 or 8, and 26 to 31
2	Never	`$AEB8` `$AEBC` `$AEC0`	Ends on frame 457 (9.1 s)	2 and 3	21 to 23
3	`$0AC8` on the title pages, and `$1320` once no voice is playing	`$B10B` `$B143` `$B0F3`	Loops every 5,376 frames (107.3 s)	7 to 10	69 to 71, 73, 75, 76 or 77, and 78

The tune table at $AA8D holds the three track-list addresses of each tune. Two pattern numbers that share an address cannot be told apart from the address, so the player shows both.

The driver is not a program of its own on the disk. Level 1's file holds it twice: once to play tunes, and once to play sound effects. $1C11 copies 19 pages of the file, from $80B4 to $A000, when the title pages are set up, and $1BE9 copies 13 pages from $747B to $B000 when play is set up. The second copy covers the first from $B000 upwards, so tune 3's track lists, which begin at $B0F3, are in the file at $91A7 and gone from memory in play.

A tune is three track lists, one for each voice. A track list is a row of pattern numbers with a few commands between them, and the pattern tables at $AAA5 and $AAF6 give each pattern's address. A pattern is a stream of notes, each with a length in frames, and commands that change the instrument. A stream picks a wave program from the table at $ACF7, and each note runs it: a short list of steps that sets the waveform and the envelope, and waits. The pulse width, the pitch slide, the arpeggio, and the filter each have a table of their own. Notes come from a table of 94 pitches at $A98C and $A9EA, where entry 45 is A3.

Stream byte	What the driver does
`$00` to `$5F`	A note, followed by its length in frames
`$60`	A rest, followed by its length
`$80`	The pattern ends, and the track list gives the next
`$81` n	Use wave program n
`$82`	Start a pulse-width sweep, from an index and a width
`$83`	Start a pitch slide, from an index
`$84`, `$8D`	Start an arpeggio, from a list
`$85`	Start a filter sweep
`$86`, `$89`	Play a drum, followed by a number and a length
`$87` n	Every note after this lasts n frames and has no length byte
`$88`	Every note after this has its own length byte again
`$8A`	Stop this voice
`$8B`	Continue at the address in the next two bytes

The commands of a pattern or sound-effect stream. The sound-effect copy of the driver reads the same commands.

Track list byte	What the driver does
Below `$F0`	A pattern number
`$F0` n	Jump to byte n of the track list, which is how a tune loops
`$F1` n	Play the next pattern n times
`$F2`	Stop the voice
`$F3` n	Transpose the next pattern by n semitones, a signed number
`$F4` n	Fade the volume out
`$F5`	Fade the volume in, from a rate and a target

The commands of a track list.

02 · Sound effects

Eleven sound effects, and the last is never asked for

In play, a second copy of the driver sits at $B000 and plays sound effects only. Press a button to hear one. The numbers are the game's own, and the names say what the levels use each effect for, where the code makes that plain.

The driver is the sound-effect copy at $B0C8, in the bytes of level 1's file from $7543 to $80B3. Each button starts the effect as a level does, with $B0EE, and calls $B176 once a frame. Each effect was checked against the same calls on the kit's 6502 simulator: 18,547 writes to the sound chip over 400 frames of each effect, in order, with no difference. The page repeats the chip's registers every 32 bytes from $D400 to $D7FF, as the chip does, so the stray writes described below land where they do on a real chip.

A level plays an effect by calling $B0EE with X set to four times the effect number. That picks a row of the sound table at $BB48, which has one byte for each voice: the number of a stream, or a value with bit 7 set that leaves the voice alone. A stream is the same kind of list of notes and commands that a tune uses, and the table at $BB74 gives each stream's address. Effects 0, 2, 6, and 7 use voice 1 alone, and the others use voices 2 and 3 together. Effect 10 plays one note and starts it again every 255 frames, so it never ends, and no level asks for it.

Effect	X	Voices	Frames	Seconds	Asked for by	Stray zero lands on
0	`$00`	1	13	0.26	Level 1: the strike, the punch, and the crouch. Levels 2, 4, and 6: walking and crouching, and climbing in levels 4 and 6. Level 3: the hit test. Level 5: taking energy.	-
1	`$04`	2 and 3	15	0.30	Darkman losing energy in levels 1, 2, 4, and 6. Level 5: the finale.	`$D4BB` no register (27)
2	`$08`	1	16	0.32	An enemy's shot in level 1. Level 5: the shots.	`$D503` voice 1 pulse width, high byte
3	`$0C`	2 and 3	23	0.46	Score pick-ups in levels 2, 4, and 6, and level 1's exit marker.	`$D4BC` no register (28) `$D47C` no register (28)
4	`$10`	2 and 3	79	1.58	Energy pick-ups in levels 2, 4, and 6.	`$D450` voice 3 pulse width, low byte `$D464` voice 1 control register
5	`$14`	2 and 3	107	2.13	A pick-up's score in levels 2 and 4, level 3's objects, and level 6's falling objects.	`$D4A7` voice 2 frequency, low byte `$D4C0` voice 1 frequency, low byte
6	`$18`	1	34	0.68	The mask game's fire button, in levels 1, 3, and 5.	`$D4F6` filter cutoff, high byte
7	`$1C`	1	11	0.22	The mask game's cursor scan, objects starting in level 1, and the shooters and blasts of levels 2 and 4.	`$D477` filter routing
8	`$20`	2 and 3	63	1.26	Level 3's objects, and falling objects in levels 4 and 6.	`$D449` voice 2 pulse width, low byte `$D47B` no register (27)
9	`$24`	2 and 3	67	1.34	An enemy dying in level 1.	`$D423` voice 1 pulse width, high byte `$D462` voice 1 pulse width, low byte
10	`$28`	2 and 3	Never ends	-	Nothing.	`$D436` filter cutoff, high byte `$D484` voice 1 control register

Voices are numbered as the player numbers them. Seconds are frames at 50.12 a second.

The effect starter has a fault. For every voice it starts, $B0EE writes a zero to one of the sound chip's control registers. It finds the register's offset in the three bytes at $B8B4, which are 00, 07, and 0E, but it indexes them with the position in the sound table, four times the effect number plus the voice, where it should use the voice. Effect 0 reads $B8B4 itself and gets the right offset by luck. Every other effect reads from the bytes that follow the table, and the zero goes to whatever address that byte gives. The last column lists them. The chip repeats its registers every 32 bytes, so a stray write at $D464 clears register 4, the control register of voice 1, and one at $D477 clears register 23, the filter's resonance and voice routing. A write at $D4BB reaches no register at all.