Spell Cast ASM

Spell Cast ASM

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Traced from EXTRACTED/mm2.asm (IRA + DC-gap decode) and cross-checked with tools/_map_spell_handlers.py / tools/_trace_spell_picker.py.

Addresses are code-hunk load addresses (Capstone base 0). A4 is set to LAB_7FFE at init (0x24948); game fields use negative d(A4) displacements.

Overview

flowchart TD
  subgraph pick [Spell selection]
    P1[JSR -$7E4E precast]
    P2[JSR -$7E12 modal picker]
    P3[JSR $6622 spell grid UI]
  end
  subgraph gate [School gate]
    G1[JSR $13730]
    G2{index in A4-$6D88?}
  end
  subgraph fx [Effect dispatch]
    CDB8[$CDB8 + table $CDC6]
    CFF8[$CFF8 + table $D002]
    STUB[Per-spell stub $B900..$C800]
  end
  P1 --> P2
  P2 --> P3
  P3 --> G1
  G1 --> G2
  G2 -->|yes| CDB8
  G2 -->|no| CFF8
  CDB8 --> STUB
  CFF8 --> STUB

Loading

Combat cast path

Combat does not draw the spell-book grid. C goes straight to the level/number prompt (-$7E12 / 0x79EE). The grid (LAB_6622) is only used from exploration cast (0x6E30) and from combat character-sheet V (0x675A).

Step	Address	IRA / gap line	Role
Player turn	0x119C2	~13501 (DC)	Combat menu loop
Command bar	0x11866	~13479	Sets A4-$5E34 if caster, not silenced, SP>0
Read key	0x1175C	~13463	CMPI #$43 accepts C
Dispatch	0x11BF8	~13538	'C' (#$43) → 0x11A90
Precast	0x11A90	~13515	JSR -$7E4E(A4)
Picker	0x11AAC	~13517	JSR -$7E12(A4) → index in D0, $FFFF = cancel
School gate	0x11AE8	—	JSR $13730(PC) with index on stack
Cleric FX	0x11AF6	—	if gate ≠ 0: JSR $CDB8(PC)
Sorc FX	0x11B02	—	if gate = 0: JSR $CFF8(PC)
SP spend	0x11B14	—	optional JSR $6DEE / refresh

Exploration / non-combat cast (0x6E30)

Readable IRA (not DC gap) — same picker, always uses $CDB8 after selection:

	LINK.W	A5,#-6			;06e30
	...
	JSR	LAB_6622(PC)		;06e8a   ; spell grid
	JSR	-32274(A4)		;06e9a   ; -$7E12 picker
	...
	JSR	LAB_CDB8(PC)		;06ebc   ; effect dispatch

JSR -$7E12(A4) — spell picker

• Call sites: only 0x06E9A and 0x11AAC.
• Not present as normal LAB_ code in the static image at A4-$7E12 (that resolves to 0x01EC, which is embedded string data in the hunk header).
• Behaves like other MM2 UI entry points (-$7BD2, -$7BE4, …): a runtime thunk in the A4 workspace that opens the Intuition/list UI.
• Nearby helper 0x6622 builds the spell list grid before/around the modal:
  • Reads A4-$85B0 (active caster context).
  • Uses A4-$8C22 (9 level labels) and A4-$8C2B (spells-per-level counts).
  • Walks known spells via LAB_65C2 / character field $51(A0) (spellbook bitmask on the live character object, sourced from roster $4C..$57 at load).
• 0x67C0 (called from spell UI setup @ 0x65B8) uses JSR -$7BD2(A4) (same key-validation family as combat 0x1175C) to step the highlight and return the chosen index.

JSR $13730 — school gate (spell_school_gate)

013730  link.w  a5,#$fffc
        ...
013744  lea.l   -$6d88(a4),a0    ; 13 x uint16 table
013748  cmp.w   (a0,d0.l), 8(a5) ; spell index from picker
        ...
        ; loop i = 0 .. 11
013766  addq.w  #1,-$2(a5)      ; if match before end → return 1
01376a  move.w  -$2(a5),d0      ; else return 0
        rts

Return	Combat branch	Meaning
1	JSR $CDB8	Picked index appears in A4-$6D88 (13 words) → cleric jump table
0	JSR $CFF8	No match → sorcerer jump table

The table at A4-$6D88 is only read here (no static initializer found in mm2.asm); it is filled at runtime when the caster/context is set up.

Effect dispatchers

Dispatch is two-stage:

1. A sparse-code executor validates/normalizes D0 and jumps by offset table.
2. The jump lands on a jsr <stub> ; bra <return> pair.

$CDB8 path (selected when $13730 != 0)

00cdb8  link.w  a5,#0
00cdbc  move.w  8(a5),d0
00cdc2  bra.w   $cfde
...
00cfde  cmp.l   #$60,d0        ; codes 0..95
00cfe8  lea.l   $cf1e(pc),a0   ; sparse offset table
00cfec  move.w  (a0,d0.w),d0
00cff0  jmp     $cff2(pc,d0.w)

• Stub pairs begin at 0xCDC6.
• There are 43 direct spell stubs in this block (0xCDC6..0xCF1A).
• Offset table at 0xCF1E is sparse; sentinel value +2 maps to return/no-op.

$CFF8 path (selected when $13730 == 0)

00cff8  link.w  a5,#0
00cffc  move.w  8(a5),d0
00d002  bra.w   $d266
...
00d266  subq.l  #2,d0
00d268  cmp.l   #$5c,d0        ; post-adjust range
00d272  lea.l   $d1ae(pc),a0   ; sparse offset table
00d276  move.w  (a0,d0.w),d0
00d27a  jmp     $d27c(pc,d0.w)

• Primary spell stub pairs at 0xD006..0xD182 (48 Sorcerer entries).
• Additional handlers at 0xD186..0xD1AA (5 extra entries) are reached via sparse table codes (these are part of the shared skill/spell engine, not a separate top-level cast menu).
• Offset table at 0xD1AE is sparse; +2 entries again mean return/no-op.

Why this matters

• The picker/gate does not pass a dense 0..47 school-local index directly.
• It passes a sparse spell code consumed by the executors above.
• A4-$6D88 in $13730 acts as a 13-entry membership/gate list over that code space (currently read-only in static analysis).

Shared exit

Spell/skill handlers live in 0xB900–0xC800; common return points are $CFF4 (CDB8 path) and $D27E (CFF8 path).

Sample stub: S1/1 Awaken (0xB66C)

Typical combat spell stub pattern:

00b66c  link.w  a5,#$fffe
00b670  jsr     $d464(pc)      ; target picker ("which monster?")
00b678  cmpi.b  #$1b,-$1(a5)   ; cancel target?
00b680  ...
00b688  jsr     $133b6(pc)      ; apply effect (level, count, target)
00b69c  jsr     $108bc(pc)      ; combat resolver / messaging
00b6a2  move.b  #1,-$7958(a4)  ; spell-acted flag

Helper	Address	Role
$D464	0xD464	Target selection UI; sets A4-$7958; 'A'..'J' monster slots
$133B6	0x133B6	Effect applier: uses caster level $71(A0), RNG -7BB4, loops targets
$108BC	0x108BC	Combat-side apply (monster count -77BE, party -524)
$6DEE	0x06DEE	Deduct SP/gems from caster at A4-$B834 after cast

spells.dat usage

• On-disk: 96 × 2 bytes cost/type (see 19-spells-and-item-use.md).
• 0xE260 and 0x13772 are equivalent spell-info render helpers:
  • both index A4-$702A (lea -$702A(a4); move.l (a0,d0*4),...),
  • print labels via -$7B84 / -$7BE4,
  • optionally print suffix at A4-$7026,
  • end with jsr -$7E84(a4) (UI/audio cue path). This is strong evidence that A4-$702A/$7026 are spell metadata text pointers (cost/type fragments) loaded before cast UI.
• Stub handlers use $133B6 / $108BC for behaviour; they do not read spells.dat directly in the stub prologue.

IRA gap navigation

Combat/spell code from 0x8000–0x248A5 is stored as DC.L in mm2.asm. To read it:

1. Generate mm2.capstone.asm: python tools/disasm_m68k.py <mm2 executable> -o EXTRACTED
2. Or run: python tools/_map_spell_handlers.py / tools/_trace_spell_picker.py

Tools

Script	Purpose
tools/_map_spell_handlers.py	Full Sorc/Cleric jump table ↔ spell names
tools/_trace_spell_picker.py	Disassemble picker, gate, stubs
tools/_trace_spell_cast.py	Earlier combat-path trace
tools/label_capstone.py	Known labels @ combat addresses

Open items

• Static body of -$7E12 (picker thunk) — needs runtime/workspace dump or second code hunk.
• Exact producer of A4-$6D88 (13-word sparse-code membership table).
• Per-stub semantics (damage formulas, status opcodes) in 0xB900–0xC800.
• Confirm A4-$702A ↔ spells.dat load buffer with a loader trace @ 0x29868 filename ref.