Ghostbusters: the source

Current truth for this game. The workflow lives in kit/skills/; how this understanding developed lives in agent-history.md. Every fact names the routine or table it comes from. Unless marked live, a fact comes from reading the code in the snapshot named in orientation.md. Live means observed in the kit's simulator (work/sim/gb.js: the whole image on the kit's 6502 with the raster IRQ, both CIAs' timers, the speech NMI, control port 1 and the keyboard); the script is named in "Live tests". Times in seconds assume PAL, 50.12 frames a second (312 lines of 63 cycles at 985,248 Hz, kit/skills/c64/c64-reference).

Build

No version or build string was found in the image; the only dated text is the title's DESIGNED BY DAVID CRANE COPYRIGHT 1984 ($3671). The file is a OneLoad64 one-file conversion of memory $0314-$FFFF (orientation.md). What is not Activision's: the hand-over at $C800 (masks the CIA interrupts, copies $C830-$C92F to $0300, zeroes $0200-$02FF, JMP $6000), and probably the machine's power-on RAM pattern the dump carries in unused memory (below, "The conversion's leftovers"). No trainer, intro or converter's credit was found.

Compared with a second copy

A cracked disk image (one file, GHOSTBUSTERS, 128 blocks, loading at $0801; its unpacker ends with JMP $6000) was autostarted in VICE and stopped at $6000 (work/d64/boot.py), and its 64 KB compared with this image as the hand-over leaves it (30 September 2026). Every region described in game.json matches, except:

• run-time values: name_entered_flag $6328 (1 there, 0 here), the operand at $8000, and 19 bytes of the speech player's own variables and operands ($F085, $F0A6, $F138, $F1BD, $F318, $F3AA, $F41B, $F41F, $F4DA-$F4E5);
• $0400-$07FF: other bytes. Bought there, the compact and the hearse show as noise in the shop (VICE screenshots); here both are whole (the Play port, same moment);
• $FD30-$FD4F: the KERNAL's vector table ($EA31, $FE66, ...) in place of speech data. Played through the speech port, phrase 3 differs in 750 of 17,768 writes; phrases 0, 1, 2 and 4 are identical.

The zero page, the conversion's own areas and the run-time buffers differ as expected.

Memory layout

$01 = $35 throughout play: RAM at $A000 and $E000, I/O at $D000 (cold_start $6022). $01 is written only at $6022, $608E/$60B4 (character ROM copy) and in the dead loader ($CE07); no code maps the RAM under $D000 in (opcodes.py --refs 0x0001).

Timing

• Raster IRQ (raster_irq $8E76, vector $FFFE), once a frame at raster $B8, re-armed at $8FC5. While speech plays ($EB) it only acknowledges. On the title ($20 = 0) it busy-waits for raster $C1 and writes $D011 with the lyric window's fine scroll ($9A), then waits for the line in lyric_split_lines $643B to put $1B back ($8EB7). In the game (irq_game $8ED4) it steps the random byte $06 (shift left, new bit 0 = bit 7 XOR bit 4), counts the tick $08, runs the bottom scroller ($9756), and in states $12 and up busy-waits for raster $DF to colour the status band (colour 6; 0 in states $2A-$2C) and for raster $EC to turn it black again. It then writes all eight sprites (x stored halved in $A0-$AF, doubled plus one on the way out, the ninth bit collected into $D010), the shapes to $57F8 with colours from sprite_colour $A949, the background from $3B, sets the frame flag $E2, and runs the music ($93F0) and the sound effects ($3BE9).
• PAL tick adjustment. The start-up measures the last raster line and sets pal_flag $EA73 ($629C-$62BD; $FF in the simulator). On PAL the IRQ increments $08 again whenever the new tick has $08 AND 7 = 1 ($8EDE-$8EEB): 8 ticks in 7 frames, about 57.3 ticks a second, near NTSC's 60 (checked by the music port, work/port/music/). The pitch table stays NTSC's: note_freq $A1F4 is tuned for NTSC (entry 57, $1C31, is 440 Hz on the NTSC clock), so on PAL every note sounds 0.65 of a semitone flat.
• Frame loop game_frame_loop $6FEC waits for $E2, then once a frame: timers and steering $7003, input $7061, idle timer $708C, pause $70BA, building colours $7106, status report $7175, ticker $71F6, PK and balance line $726D, typewriter $72BD, line input $7347, shop credit $7399, building timers $73BD, PK rise $73F3, new hauntings $740C, and the state handler through $381A ($746D). While a text page is typing or a line is being typed the loop returns before the timers.
• Title loop $6305 waits for raster $28 each frame; on PAL it runs the tune and lyric tick twice in one frame of eight ($6338-$6348).
• Speech NMI. The speech player points the NMI vector at $F0C3 and runs CIA 2 timer B with latch $0065 ($F47E-$F48F): an NMI every 102 cycles, 9,659 samples a second on PAL (10,027 on NTSC). The game waits for a phrase to end ($8DB9 polls the player).
• Game clocks in frames: PK +1 every 64 frames below 1000, every 32 in the 1000s, every 16 from 2000 (frame_pk_rise $73F3); building timers every 256 frames ($73BD); map sprites move 2 pixels on frames where $09 AND $3C is 0, with $3C from pk_rate_masks $9DBA by the PK's thousands digit ($3F, $1F, $0F, $07, $03, then $01): every 64th frame below 1000, every other frame from 5000 (map_move_sprites $7C85).

Controls

Joystick in control port 1 only (read_joystick_port1 $96CA, $DC01 bits 0-4 into $33); the keyboard scan $96E8 (row selects $3753, column masks $374B) gives a key code (column × 8 + row) in $19 and a PETSCII character in $17, and gives up while either port reads other than $FF. These two are the only readers of CIA 1's ports.

Graphics

• VIC bank 1 ($DD00 bits 0-1 = %10, $6033). Screen $5400, character set $5800 ($D018 = $56), sprite pointers $57F8. The start-up clears $4000-$5FFF ($6048-$6058) and rebuilds it: sprite shapes from the packed stream, the upper-case character ROM copied to $5808-$5BFF, 128 bytes of glyphs from $36A4 over characters $1B-$2A (the ACTIVISION logo, TM, $, %, ', !), and the letter O's shape copied over the digit 0 ($60C1-$60CA). In the lyrics and end texts ( is drawn as ! (character $28 from $370C).
• Packed sprites. rle_unpack $610B expands $B408-$BFF7 into $4000-$4ED7, sprite shapes 0-59: the byte $11 followed by n writes n zeros (0 means 256), any other byte is copied; it stops when the source reaches $BFF8, so shape 59 gets only its first 8 rows and the 8 bytes at $BFF8 are never read. build_mirrored_sprites $6151 makes left-right mirror images of the 8 shapes at $4640-$483F into $4F00-$50FF through pixel_mirror_table $E700 (a 256-byte table that reverses the four 2-bit pixels of a byte, built at $605A).
• Cars. Each car picture is 12 × 16 multicolour characters of which the image stores the left 6 columns ($0200, $0500, $0800, $0B00); build_car_charset $7667 writes them to $5A00 and their mirror to $5D00. Bought equipment is painted into the car picture (shop_paint_item_in_car $793E, through the mask table $E600), and the picture is kept at $E000 for the drives ($7AC8, $8007).
• Scenes. The title copies its own character set ($6960-$6F5F) to $5A00; the map copies $2A50; a building copies six pages from $1FA8 (Zuul: $0F80) (st17_draw_building $82AF), with the front layout chosen by bldg_attr $A1C0 bits 6-7. Zuul's climb scrolls the screen down a row per step ($3300): 176 steps of three repeating tower rows, then the 21 rows of the temple top, 197 in all (live, agent 2).
• Map colours. frame_colour_buildings $7106 recolours five of the twenty buildings a frame from $3EE2 by the state's colour bits: 0 green ($0D), 1 purple ($0C), 2 white ($09), 3 red ($0A); red alternates with green every 16 frames (live: adddd… in the colour RAM, 16 frames each).
• Bottom row. Row 24 carries the scroller ($3624, 128 characters) and the Activision logo as sprite 7 recoloured per raster line from $3714 ($9756, $97A1), or in play the ticker and CITY'S PK ENERGY: line.

Mechanics

The game state

$3A indexes the 64-entry word table state_handlers $381A (frame_dispatch_state $746D); a handler ends at next_state $8D86 ($3A + 1) or stay_in_state $8D8D.

The three endings, live: foreclosure $2D → $3B-$3F → $39 → $3A (phrase 3); win $2C → $36 → $37 → $38 → $31-$35 → $39 → $3A; GOOD TRY $2E → $2F → $30 → $31-$35 → $39 → $3A.

Money

Six BCD digits $57 (high)-$59. money_add $9664 saturates $57/$58 at $99 (live: $999900 + $2000 stays $999900); money_subtract $9636 stops at 0 (live: $2500 − $4000 = 0); money_compare $9654 tests affordability. A new franchise starts at $10000 (st02, $57 = $01). Prices: cars car_price_mid/_high $A1D4/$A1D8 ($2,000, $4,800, $6,000, $15,000); equipment item_price $A1DC in hundreds ($400, $800, $800, $400, $600, $600, $500, $8,000 for items 0-7). Item 4 (shape $37, $600, no flag) is on no shelf (shelf_shapes $AAB3), so it cannot be bought. Its unpacked shape, between the bait ($36) and the trap ($38), has the trap's base and row of dashes under two raised flaps. POKE 38454,96 makes money_subtract an RTS: every purchase and the Marshmallow Man's charge become free (live: the hearse for nothing, agent 6; $10,000 kept through a stomp, t20-poke-mm.js).

Equipment

$6D holds a bit per item from item_flag $A9A8: detector $01, image intensifier $02, marshmallow sensor $04, bait $08, vacuum $20, laser confinement $40; traps are counted ($6A owned, $6B empty), bait in dollops ($69, 5 per purchase). shop_fire_at_car $78D8 refuses at the capacity car_capacity $AA9A (5, 9, 11, 7) with message 7, YOUR CAR IS LOADED TO CAPACITY. (live: load 9 in the hearse refused, 8 accepted). A trap's shelf refills, so traps can be bought up to the capacity; the status report prints $6B as one digit, so 10 and 11 empty traps read : and ; (live by poking; a wagon and a balance of at least $12,000 would reach 10). The image intensifier's flag $02 is read by slimer_update $9AA6 in every bust state: without it the Slimer (sprite 4) gets background priority ($D01B bit 4) and disappears behind the building's foreground colours; with it he is drawn in front (live: $D01B $10 without, $00 with, and the pictures show the Slimer cut by a window without it). The six readers of $6D are $76F5 (the shelves), $7923 (the purchase), $7D79 (the warnings), $81C7 (the vacuum), $87C9 (the laser confinement system) and $9AAC (opcodes.py --refs 0x6D).

PK energy

Four BCD digits $5B/$5A, capped at 9999 (pk_add_hundreds $9895, $98E3). It rises by itself (Timing) unless the Zuul phase has begun ($81); +100 for each Roamer that reaches its target on the map (st12_city_map $7BB7-$7BCB, live: 0007 → 0108); +300 for a Slimer that escapes, by the timer ($73D9, live: 0007 → 0311 in 255 frames, control without it 0007 → 0011) or after a missed trap ($8704, live, agent 5). Every time the thousands digit changes to 5 or more, by any addition, $98AD-$98DB picks a building ($EA74 low nibble, at least 4, skipping Zuul $0A and flattened blocks) as the Marshmallow Man's, $80, state $C8 (live: a Roamer taking 4950 to 5050 marked building 6). The thousands digit also sets $3C, which speeds up the map sprites, the PK rise and the number of new hauntings.

Buildings

Twenty buildings, index $6E 0-19 (GHQ $11, Zuul $0A), each a state byte $C8+x: high nibble a timer, bits 2-3 the stage, bits 0-1 the colour shown.

• New hauntings (frame_spawn_haunts $740C): when no building is in stage 0 with its timer running, 1 to 3 (more as PK rises) free buildings are picked from the random byte and set to $10.
• Ageing (frame_building_timers $73BD, every 256 frames in states $12 and up, so also while driving and busting): +$10; a timer that wraps moves the building on by bldg_next_stage $A9B4: stage 0 → $14, stage 1 → $1C, stage 2 → $F8, stage 3 → $1F; a state of exactly $xF → $FF + 1 is the escape (+300 PK, state 0). The CMP #$0F admits only the haunted state; $xD/$xE are never produced. Live life of one haunting from $10, no input: stage 1 after 3,839 frames, stage 3 after 7,679, haunted ($1F) after 11,519, escaped after 15,359 (5 min 6 s); 15 ticks of 256 frames (76.6 s) a stage.
• Warnings (map_building_under_logo $7D23, every frame on the map): only buildings whose rectangle ($37D3 columns, $37DD rows, each including the streets around the block) holds the logo keep a colour. For each of those the colour becomes its stage when warn_needs $A9B0[stage] is owned in $6D: stage 1 purple with the PK energy detector, stage 2 white with the marshmallow sensor, stage 3 with the detector turns the building haunted at once ($1F, its timer restarted at 1); otherwise 0. Every other building loses colours 1 and 2 (a low nibble of $0C or more is kept, so haunted buildings stay red everywhere). Live: stage 1 building 15 turned purple ($35, colour RAM $0C) with the detector and the logo on its street, stayed green without the detector or with only the sensor, and went back to $34 when the logo left; the Marshmallow Man's building $C8 turned white ($CA, $09) only with the sensor and only near the logo; stage-3 building 8 ($3C) became $1F with the detector near it.
• Where a Slimer is. The bust tests stage bits %11 (st18_carry_trap $8505, bust_check_slimer_present $9A8A), which accepts $xC to $xF: a stage-3 building that has not turned red yet already holds a Slimer. Live: at the bust set-up $8C, $8D, $8F kept the Slimer; $84, $88, $00 sent the men home. The map lets the player drive to any building (map_fire_select $7E55 does not look at the state) if there are empty traps (message 0), at least two men (message 1) and backpack power (message 3) (live, each refusal).
• Reward (st1F_trap_closes $87DB-$8801): slimer_reward $A1E4[state >> 4] hundreds when bits 2-3 are %11 (the building is then cleared), else index 15, $300, and the building is left alone. The table is $1,000, $1,000, $900, $900 … $300, $300, so the fee falls $100 every two timer ticks (10.2 s) the building waits. Live, the state poked just before the trap closed: $1F $1,000, $2F $900, $5F $800, $AF $500, $FF $300, $1C $1,000, $6C $700, $00 $300, $34 $300 (building left at its state). The timer restarts at 1 when a stage-3 building turns haunted, so a hidden stage-3 Slimer is paid by the time since stage 3 began.

The busting

From agent 5's reading and runs (states $18-$21): fire sets the trap down only at a Slimer's building; man 1 then man 2 are placed; with the streams on and the men 12 or more apart the stick only closes the gap ($85B9-$85D2, auto_joystick $B3AD, live); men facing each other closer than $2A − |dy|/4 cross the streams ($85D4-$8615): a 64-frame freeze, backpacks 0, two men lost, message 8, the Slimer escapes (live: men 3 → 1). Power drops 1 (BCD) every 16 frames with the streams on (live: 85 → 28 in 900 frames); at 0 the trap springs. The trap catches the Slimer within x −8…+7, y −12…+3 of its light before the light timer $7A reaches $9C ($86B3-$86F7, trap_hitbox $A9A0); a miss slimes a random man (men − 1, phrase 2, +300 PK, live). With the laser confinement system a catch goes to storage $6C (up to 10) instead of an empty trap ($87C9-$87D9; live, t18-laser.js: stored 0 → 1 and 9 → 10 with the traps untouched, at 10 an empty trap used). A building without a Slimer: the men leave when the delay $7C ($7F) runs out ($9A8A → $8823).

GHQ

st22_ghq_restock $88B6: stored ghosts 0, empty traps = traps owned, men 3, backpack power 99 (live, agent 5).

Roamers and the drive

Roamers are map sprites 4-7, aimed at Zuul ($62,$7A) from $37C3 (st10_map_setup). One within about 8 pixels across and 13-17 down of the logo is marked with the route length so far (map_roamer_contact $7DAA) and is met on the road at that distance (st15_driving $8117-$817A), two at a time at most. The drive's length is the route's dots + 5 road lengths ($67, $8001); the car accelerates 1 a frame to car_top_speed $AA9E ($60, $70, $80, $A0; the options text says 75, 90, 110, 160 mph) and brakes on arrival. The vacuum ($818C-$8274) needs $6D bit 5 and a new press of fire with the Roamer within x −32…+15 of it; the Roamer is pulled in, a 32-frame countdown runs, and it restarts on the map ($9851). No money, no PK change. Live: owned, fire at x 31 against 63: countdown from frame 5199, sent home at 5230; not owned, the same fire does nothing.

Every drive leaves two bytes on the stack: state $14 enters next_state by JSR ($8070), and nothing pulls them (live, agent 5).

The Marshmallow Man

When the building in $80 has aged to $F8-$FB (map_marshmallow_check $7ED8; the pick sets $C8, so 769 to 1,024 frames, 15 to 20 s, later) the alert starts: the state is cleared, the Roamers are sent to four points around it, the bait flag $68 is cleared, -MARSHMALLOW ALERT- (message 4), state $24. During the gathering the map code keeps running, B included ($8925 → $7F29 → $7F70); B takes a dollop and, if none is down, draws bait under the logo and sends the Roamers to it instead. When all four stand on their targets: bait down → state $26, MAYOR AWARDS YOU $2000… (+$2000); none → state $25, the building is flattened in four steps ($EA28[x] = 0) and $4000 deducted (message 5). Live (t7-marshmallow.js): no B, $10,000 → $6,000 and the block flattened; B 20 frames after the alert, $2,500 → $4,500, dollops 5 → 4, the block kept; B with no dollops, SORRY, NO BAIT. and the stomp; bait dropped before the alert only, the stomp (the flag is cleared at the alert).

$80 holds one building. If the next thousand is crossed before the alert, the new pick replaces it and the old building stays at $F8 for good: stage 2 ages into $F8 again (bldg_next_stage), it is never haunted, never stomped, and shows white near the logo to a sensor owner (live, t17-mm-orphan.js: $F8 held for 3,000 frames). In the eight runs from PK 5000 above no alert came at all, the picks replacing each other as Roamers pushed PK up by thousands.

The Keymaster, the Gatekeeper and the end of the game

Map sprites 2 and 3 wander the street grid, choosing the next crossing from the random byte (map_gatekeepers_wander $7DFF). From PK 5000 ($5B ≥ $50) each is sent to Zuul ($3802) when it passes its own crossing $37FE; from 9500 ($5B ≥ $95) both are sent at once (st12_city_map $7BF8-$7C2C). When both stand on Zuul (map_zuul_meeting $7C2E), once: a balance below the starting balance $51-$53 (a byte-by-byte CMP, so an equal one passes) → the foreclosure pages; otherwise the Zuul phase ($81 = 1): GO TO ZUUL!… (message 9), the logo drives itself to Zuul, every building state 1 each frame and Zuul $0F (red); the steady PK rise and new hauntings stop ($73F3, $740C), Roamers still add 100 on arrival (PK 9999 on the status line in t14-endings.js). Live (t6-keymaster.js, t6b-keymaster-spread.js, t14-endings.js): from 9500 they met 188 frames later at 9711 (two Roamers arrived meanwhile); from 5000, eight runs met at PK 8495, 9511, 9519, 9524, 9718, 9724, 9725 and 9999, within 1,526-1,999 frames, most of the rise being Roamers reaching Zuul; $2,500 against $10,000 foreclosed (phrase 3, STARTING BALANCE: $10000, ENDING BALANCE: $2500); an equal balance opened the Zuul phase. PK 9999 is the cap, not the trigger.

A non-decimal starting balance can never be matched: a blank name with 458 decodes to $57 = $A0 (YOU HAVE $:00000, live); buying the high-performance car leaves $985000 (the 6502's decimal subtract treats $A0 as 100), and money_add saturates at $99, so the meeting always forecloses (live with $999900 against a start of $A00000).

Zuul

st28_zuul_street_setup $8A2C / st29_zuul_street $8B07 (agent 5): men reset to 3; $EA78 = 2 men must reach the door (x $5B-$5E at the pavement line, $8ACC-$8AD4); $EA79 = 2 catches end the attempt (GOOD TRY). A catch is a hardware sprite collision ($D01E AND $2F, sprites 0-3 and 5) tested every 4th tick; the Marshmallow Man walks a 32-step path to and fro (mm_path_y/_x/_frame $A8A5/$A8C5/$A8E5). Two men in: the climb (197 steps), then st2C_close_portal cannot fail and pays $5,000 (live: $2,500 → $7,500).

Endings and the account number

GOOD TRY is shown when the Marshmallow Man catches two men on the Zuul street ($8B10); it and the win both go on to the credit limit (the balance with $59 zeroed, $8CAC) and a new account number ($8CC6). Both print YOU MADE MORE MONEY THAN YOU STARTED WITH, true only as "not less" (see the meeting test). After F1/F3 at the end the game cold-starts ($8D36), which keeps $6328 and $EAC7-$EACA, so F3 then starts with the account just shown (live, agent 5: $7,500).

The account number (encode account_encode $90EE, decode account_decode $9155, parse account_parse_digits $9CFC; live, agent 6 and t11-account.js):

1. Balance in hundreds: hi = $57, lo = $58 (BCD); $59 is dropped.
2. Name sum s = the 20 bytes at $EAB3 (the name as typed, PETSCII, zero-padded) added modulo 256 (account_name_sum $91B6).
3. Check byte: c = (hi + lo) mod 256, 1 if 0; step s times (256 when s is 0) the LFSR account_lfsr_step $91A6: c shifted left, new bit 0 = bit 3 XOR bit 4 XOR bit 5 XOR bit 7 of the old c.
4. N = hi × 65536 + c × 256 + lo, 24 bits, as eight octal digits o7…o0; the four bytes $EAC7-$EACA each hold two of them and are printed in order, so the number reads o1 o0 o3 o2 o5 o4 o7 o6.
5. Typing: the low nibble of each of up to 8 characters is packed into $EAC7-$EACA; decode keeps the low 3 bits of each, so 8 reads as 0, 9 as 1, and letters count by their PETSCII low nibble (the line input

lets them through: LEFTY for the name LEFTY gave $860,000, live, t19-letters-trap.js); a wrong check byte gives 0, and 0 is INVALID ACCOUNT NUMBER. ($7523). The decoded balance is not checked for decimal digits.

Live: STANTZ,RAY (sum $FC) with 03452601, computed from the model above for $54,300, gave YOU HAVE $54300; 03452602 was refused; VENKMAN,PETER with 64405104 gave $123,400 and 64485184 the same (agent 6); a blank name with 614 gave $300,000. With an 8-bit check, about one number in 256 passes for any name, and names with the same byte sum share every account.

Data tables

Sound

• Music (music_play $93F0, music_restart $93E2), Russell Lieblich's arrangement: three track lists ($A2BD melody, $A32B bass, $A399 percussion, 109 pattern numbers each), 71 patterns at $A407 (control byte: length in ticks, rest, tie, note, optional instrument and master volume), pattern pointers $A75B, 9 instruments $A7EF (pulse width, waveform, ADSR, vibrato depth). New events every fourth tick ($08 AND 3). Patterns 51 and 52 are valid and never played. Called from the IRQ each frame; $47 bit 7 (pause) stops it. music_voice3_busy $9593 keeps it off voice 3 while a sound effect plays ($98). music_skip_ahead $63D7 keeps the tune and lyrics in step, silently, while the title speaks.
• Sound effects on voice 3 (sfx_tick $3BE9, sfx_start $3D24): a bytecode, low nibble the command (wait, gate + note, sub-commands, note, trill, loop count, pulse width, waveform, bend, end); five scripts ($3DB4/$3DB9). Effect 0 is the vacuum ($8218), 2 the forklift ($7867), 3 started at $867C; effects 1 and 4 are never started. The typewriter clicks voice 3 directly ($72BD).
• Speech (speech_call $F080 → $F42E; A = phrase, $FF status, $FE stop): 4-bit samples written to $D418 by the NMI (Timing). Speech is built from pitch periods: a waveform chunk played forward, then backward, then a silent gap whose length sets the pitch ($F083, $F0A4, $F0C3). Frame records (4 bytes) choose voiced frames (4-bit samples, the waveform moving halfway to each new chunk, $F3FC) or unvoiced ones (1-bit noise, $F372). Five phrases ($F4EA); lengths 0.938, 1.568, 1.315, 2.681 and 2.223 s (the speech port, work/port/speech/, which matches the game's 311,368 $D418 writes); 8.73 s of speech from 2,738 bytes, about 15 times smaller than the same speech as raw 4-bit samples. The game plays phrase 1 (start-up, title SPACE, a catch), 2 (a man slimed), 3 (start-up, a man caught at Zuul, the foreclosure) and 4 (the portal); phrase 0 is never asked for. Which words each phrase says is not settled from the code: phrase 1 is "Ghostbusters!" (the title speaks it on SPACE, as the manual says); 2 as "He slimed me!" and 3 as the laugh are inferred from where the game plays them and their sound pattern (nine voiced syllables in 3); 4 is unknown. A pitch record's period count is 32 - (bit 0 of byte 0 x 16 + byte 1's high nibble) ($F33B-$F344). The player refuses to start with the KERNAL ROM banked in ($F45F).

The conversion's leftovers

• The hand-over $C800 and the page image $C830 (orientation.md).
• A turbo tape loader at $CE00-$CED9, never run, whose RESTORE handler ($CEC1) would fill memory with $02 (a JAM opcode) from $0202; a call chain at $CF80 (JSR $CE00, $0A00, $CE00, $0E00) that nothing reaches. In this image $0A00 and $0E00 are car graphics. That these are the original tape's loading sequence is an inference.
• The power-on RAM pattern at $C000-$C7FF, $C930-$CDFF, $D000-$DFFF (RAM under I/O) and $EB79-$EFFF.
• The image's bytes at $4000-$5FFF, overwritten at start-up.
• Unused in the game's own code: sprite_y_distance $9C76 and set_balance_10000 $9CF1 (never called); three-NOP runs at $90D1, $90DB and in map_roamer_contact for sprites 2-3; $8D90-$8D95; $EA88 read at $8832 by a branch to the next instruction; the dormant restart timer $14 ($70F8); the unreachable $02 = $C0 branch ($7094); sound effects 1 and 4; speech phrase 0 and the 2-bit speech decoders $F267/$F3E2; item 4 ($37) with a price and no shelf; unused_aadd $AADD, unused_flags_copy $AACB.
• POKE 22014,9 ($55FE, "unlimited lives" in cheat lists) lands in the screen at $5400, which the start-up clears; nothing reads it (agent 2, seven states for 900 frames each).

Live tests

All in the simulator (work/sim/gb.js) from its saved states; the scripts are in work/verify/ unless another folder is named.

Cheats

Pokes that change the game within its own parameters. Each one names the variable it changes and whether it has been tested live. Untested pokes are labelled as candidates.

POKE 22014,9, given as "unlimited lives" in cheat lists, does nothing in this copy: $55FE is in the screen at $5400, which the start-up clears and rebuilds.