LLBCS 32-team ROM hack

Locked target: 32 teams × 20 players, 32-team bracket, 256 KiB PRG + 128 KiB
CHR, MMC1, emulator-first. Stock 16-team path must keep working.

Repo root: /Users/dfm/GitHub/nesdav/little-league
Base ROM: Little League Baseball - Championship Series (USA).nes
Report: docs/AUTORUN-REPORT.md · Plan: docs/PLAN-32-TEAM.md

Build chain

BASE="Little League Baseball - Championship Series (USA).nes"
.venv/bin/python tools/expand_rom.py "$BASE" -o build/32x20.nes
.venv/bin/python tools/build_32x20.py build/32x20.nes data/roster.json -o build/32x20-ui.nes
.venv/bin/python tools/build_select_screen.py build/32x20-ui.nes data/teams32.json -o build/select-screen.nes
python3 tools/build_dispatcher.py build/select-screen.nes -o build/dispatcher.nes
.venv/bin/python tools/build_bank11.py build/dispatcher.nes -o build/bank11.nes
.venv/bin/python tools/build_bracket_screen.py build/dispatcher.nes -o build/bracket-screen.nes
.venv/bin/python tools/build_bracket_input.py build/bracket-screen.nes -o build/bracket-input.nes

build_bracket_screen.py owns bank 11's code/data, so it replaces the bank-11
logic image. Use --loop-to 0x8100 when input code will be added, and
--seed-human N only for test builds (production reads $07C3).

Never commit build/ or *.nes. Build outputs are gitignored on purpose.

Bank map (expanded ROM)

Bank	Use
8	32 rosters, 32×$170 bytes, pointer table $7F00
10	32-team selector
11	bracket scene: screen $8000, input $8100, seed $8200, bracket table $A000, codes $B000, palette $B100, list $B200
15	fixed bank (was 7 in stock)

Only $C000–$FFFF is fixed. Any address $8000–$BFFF needs a bank tag.

State map

Address	Meaning
$07C0–$07C2	selector page / cursor
$07C3	selected team ($FF = none)
$07C6–$07C9	pad scratch + edge state
$04EB/$04EC	alive flags ($80)
$04EF/$04F0	raw team IDs for the two sides
$047B	scene index; stock field = 3
$047C	frame/scene tick
$047D	vblank handshake
$04E6	scene-transition request
$C1	game/mode flags; stock field $76
$0746	matches completed
$074B/$074C	16-bit result bits
$7700	63 bracket slots (cart RAM)
$7740	32 win counts
$7760	round / match

Stock field state observed: $04EF=$0D (Italy), $04F0=$02 (Pennsylvania),
$047B=$03, $C1=$76, $0746=$0000.

Stock menu path

Team select's prompt is not confirm/cancel:

• CONTINUE = keep editing teams → back to map
• END = finish selection

Full path to a field:

team select → END → PASSWORD → A → matchup
→ A → SPEED MODE / WATCH THE GAME → down + A
→ pre-match cutscene → field

Directly poking the field state from the 32-team bracket returns to the bracket;
the missing piece is the pre-match/scene init routine, not the handoff values.

Traps that already cost time

1. $CBE6 is not an entry point. It is LDA #$00. Hooking it with JSR
   makes STA $2001 use the wrong A. Hook at $CC06 (STA $2000) after reset
   init, and have the trampoline re-execute STA $2000.
2. PRG RAM writes are dropped before CHR0 bit 4 is cleared. Call
   LDA #0; JSR $C11C before touching $6000–$7FFF.
3. NMI corrupts timing-sensitive cart-RAM writes. Disable with
   LDA #0; STA $2000 immediately before the 32-team seed; re-enable before
   JMP $CC09.
4. Every display-list team code must be 3 bytes. "NY" shifted every later
   run by one and sent the flush down the RLE path. Pad with
   code.ljust(3)[:3].
5. Custom byte builders must size zero-page operands as 2 bytes.
   CMP $02 is 2 bytes, not 3. Mis-sizing silently shifts branch targets.
6. $04EF/$04F0 are raw team IDs — confirmed by the bank-1 name renderer
   at $AF40, which indexes team-name pointers with them.
7. Do not write $C040. It is a ROM byte ($40) used by BIT as a bitmask;
   the flush checks bit 6 of each run's high byte for RLE.
8. jsnes 1.2.1 has an MMC1 shift-counter bug. Use fceumm through romdev for
   real mapper behavior.

Verification

.venv/bin/python tools/verify_regression.py \
  "Little League Baseball - Championship Series (USA).nes" build/32bracket.nes

Expected: screenshots MATCH, system_ram differs in 0 bytes.

romdev checks that matter:

• selector renders after reset init
• bracket leaf 0 shows the seeded human (FLA for human 15)
• $7700..$771F is 32 unique values, human at slot 0
• stock field reachable through the menu path above

Current status

• 32 rosters and selector: working.
• 32-team seed + names: green ($07C3 → $7700, human at leaf 0).
• Scene dispatcher: fixed hook at $CC06, committed.
• Game launch from the 32-team bracket: open. Best next step is capturing the
  stock password→matchup→field init, not poking more state.