Crystal/docs/NATIVE_PORT.md

Native port status and reference checks

Reproducible reference

The private .reference/pokecrystal checkout is pinned to 7a7881d0d62e0ddbd82dcf10e7116807487ac651. With RGBDS 1.0.3, its crystal11 build is byte-identical to the supplied English US/Europe revision 1.1 ROM. npm run check:reference verifies the files and commit. It checks every ROM and RAM address in src/game/rom/profile.ts against generated symbols, event constants against constants/event_flags.asm, and map-group bounds against data/maps/maps.asm.

To recreate the private reference:

git clone https://github.com/pret/pokecrystal.git .reference/pokecrystal
git -C .reference/pokecrystal checkout 7a7881d0d62e0ddbd82dcf10e7116807487ac651
make -C .reference/pokecrystal crystal11 -j4
npm run check:reference

Install RGBDS 1.0.3 separately. No script downloads a game ROM. CRYSTAL_ROM_PATH optionally selects another local location; checks otherwise use Pokemon - Crystal Version (UE) (V1.1) [C][!].gbc at the root.

The reference checkout, rebuilt ROM, extracted graphics, saves and gameplay screenshots must stay local and ignored. The shipping profile contains addresses and format constants, not game content.

Routine map

These paths refer to the pinned PRET source.

Native module	PRET reference	Evidence and limits
game/rom/lz.ts	home/decompress.asm	All LZ command types have unit vectors; six tilesets match original ASM execution byte-for-byte.
game/rom/assets.ts maps/events	data/maps/maps.asm, data/maps/attributes.asm, data/maps/scenes.asm, data/maps/landmarks.asm, macros/scripts/maps.asm	Any map header in the ROM's 26 groups decodes; only maps explicitly listed in NATIVE_MAPS can be entered. Location names, scene-variable owners and connection offsets come from the ROM.
Tiles/palettes	home/map.asm, engine/gfx/color.asm, engine/tilesets/mapgroup_roofs.asm	Graphics match rebuilt reference bytes. Connected maps draw beyond the edges with the current tileset, like the original strips. Native tileset animation and special palettes; Johto, Ice Path, restless Ilex Forest and Tin Tower each match 96 reference VRAM frames. 192 palette cases match the original routine.
Sprites/rendering	data/sprites/sprites.asm, data/sprites/facings.asm, data/sprites/emotes.asm	Chris/Kris, standard NPCs, emote bubbles and jump shadows decoded. Walking frames follow SetFacingStepAction. Variable sprites and Pokémon icons decoded; grass priority supported. Owned room decorations support selection, removal, slot placement, descriptions and validated saves.
game/world/world.ts	engine/overworld/events.asm, player_movement.asm, warp_connection.asm, data/collision/collision_permissions.asm	30 Hz overworld ticks, 8-tick walks, 16-tick ledge jumps, directional mats, animated door/stair exits, connection coordinates, events, scenes and callbacks. NPC random walks and spins follow HandleNPCStep. Forced movement, Surf, Cut, Strength, cycling rules, pits and elevators implemented. Fourteen reference traces compare turn timing, actors and event flags; map-entry boundaries verify the completed destination. Bicycle access uses the Key Items menu (Select) or the pack.
Event interpreter	macros/scripts/events.asm, engine/overworld/scripting.asm, engine/events/std_scripts.asm	Resumable; yields text, choices, movement, emotes and pauses. Scenes, phone contacts, string buffers and object commands. Unknown commands and specials abort without committing.
Movement interpreter	macros/scripts/movement.asm, engine/overworld/movement.asm, engine/overworld/map_objects.asm	Turns, steps, slides, jumps (two tiles with the original arc), sleeps, facing locks, visibility and emotes. follow takes one tile toward the leader's previous square. All movement opcodes decode, including teleport, fishing, skyfall, shake and flicker poses; Controlled reference scenes check spin, teleport, skyfall, fishing and flicker direction, visibility and lift.
Specials	data/events/special_pointers.asm, engine/rtc/timeset.asm, engine/overworld/decorations.asm	Selected by routine address from the ROM table: SetDayOfWeek, initial DST flags, RestartMapMusic (no audio yet), room decoration toggles, PokemonCenterPC and PlayersHousePC (Bill's, the player's and Oak's PCs), the Town Map, HealParty, HealMachineAnim (presentation only), CheckPokerus and the StubbedTrainerRankings_Healings stub.
game/scripts/pc.ts	engine/events/pokecenter_pc.asm, engine/pokemon/bills_pc_top.asm, engine/pokemon/bills_pc.asm, engine/events/prof_oaks_pc.asm, engine/events/std_collision.asm	The Pokémon Center and house PCs: Bill's PC (deposit, withdraw, release, change and name boxes), item storage, the empty mail box and Oak's rating. Menu strings and texts come from the ROM; lists are native. Moving Pokémon, the stats screen and printing are not ported.
game/scripts/start-menu.ts	engine/menus/start_menu.asm, engine/pokemon/mon_menu.asm, mon_submenu.asm, party_menu.asm, switchpartymons.asm, engine/items/pack.asm, engine/items/item_effects.asm	The start menu, the party menu with the Pokémon submenu (STATS, SWITCH, MOVE, ITEM) and the pack (USE, GIVE, TOSS) with the field item effects listed below, including Rare Candy, stones and vitamins. Menu strings, prompts and texts come from the ROM; screens are native. Field moves from the menu, MAIL, SEL and the other field items give a notice.
game/scripts/evolution.ts	engine/pokemon/evolve.asm, engine/pokemon/learn.asm, engine/movie/evolution_animation.asm, engine/pokemon/party_menu.asm	EvolveAfterBattle/EvolvePokemon over the raw evolution bytes, the evolution texts and a timed, B-stoppable picture sequence, UpdateSpeciesNameIfNotNicknamed, CalcMonStats and the HP rise, LearnLevelMoves, LearnMove/ForgetMove outside battle and PlacePartyMonEvoStoneCompatibility.
game/rom/pokemon.ts	data/pokemon/base_stats, evos_attacks.asm, data/moves/moves.asm, data/items/attributes.asm, engine/gfx/load_pics.asm	Species, move and item names, base data, evolution lists, learnsets, move PP, item pockets, growth-rate exp and front pictures (FixPicBank, PadFrontpic). Starter pictures match rebuilt bytes; all 251 evolution lists match the pinned source.
game/party	engine/pokemon/move_mon.asm, engine/pokemon/caught_data.asm, engine/items/items.asm	GeneratePartyMonStats for script gifts: DVs, FillMoves, PP, exp, CalcMonStatC, happiness and caught data. PutItemInPocket, key items and TossItem. SendMonIntoBox, SendGetMonIntoFromBox (deposit and withdraw), RestorePPOfDepositedPokemon and CalcLevel for the PC's boxes and item storage. TMs and HMs are refused.
Text interpreter	macros/scripts/text.asm, constants/charmap.asm, home/text.asm	Literal/far text, RAM names and string buffers from native state, numbers of dots, and sound or pause cues (consumed). text_asm and other RAM reads are refused.

Supported event opcodes are explicit in the interpreter switch. Audio commands consume their operands, but sound sequencing is pending; those opcodes do not imply complete audiovisual behavior. pause holds the current text or waits the original number of overworld ticks.

Scripts run on a private draft. The world presents each yielded effect, then resumes the script with the player's answer or when the animation ends. The draft is committed only when the script ends. A save made during a scene returns the committed state, and coordinate events rewind to the source of the triggering walk or two-tile jump. Saves during movement also retain the source tile until arrival events run, including across map connections. A failed scene restores the positions it had changed. As in LoadMapObjects, map objects spawn when the map loads. Later flag changes do not remove objects already shown; only appear and disappear do.

The opening scenes currently run end to end from the ROM: Mom's Pokégear, weekday and DST scene, the teacher at the west edge, the rival at the lab window, Elm's introduction with its yes/no loop, the lab's exit guard, the starter choice with pokepic, givepoke and the nickname prompt, Elm's directions and the aide's Potion through the ROM's own GiveItemScript. callasm accepts only explicitly empty routines or native translations: HalveMoney, GetWhiteoutSpawn, the item ball's TryReceiveItem and the fruit tree routines. The naming screen is a native text field limited to the characters the original offers.

Actual emulator comparison

tests/reference-parity.spec.ts loads the user's ROM into the reference emulator and places a small original test trampoline in emulated WRAM. It calls the ROM's FarDecompress routine at $0b40, then sets a return sentinel. Every output byte is compared with the native decoder for six supported map tilesets. This executes the original routine rather than comparing two copies of our code.

The same suite compares 400 damage cases and 400 type-effectiveness cases per browser against the original battle routines, 300 CalcMonStats cases (with and without stat experience, including levels above 100 that reach the 999 cap) and every CalcExpAtLevel value for the six growth rates and levels 1–100. Battle unit tests cover win, escape, loss, experience, level-up and move-learning flows, and tests/playthrough.test.ts plays the whole opening quest from a new game through GameWorld's inputs, with save/reload after each stage. This establishes parity only for the compared routines and inputs. It does not prove complete gameplay, rendering, battles, audio, timing or physical-device parity. Extend controlled comparisons as each subsystem is translated.

tests/reference-random.spec.ts also executes the unpatched BattleCommand_Critical, BattleCommand_CheckHit and BattleCommand_DamageVariation routines. The original Link RNG and the native random callback start from the same ten-byte stream. Each case compares the result, modified accuracy, miss damage and final RNG stream/cursor, covering skipped draws and rejection sampling across stream regeneration. Each browser runs 2,560 critical cases, 2,914 accuracy cases and 2,149 damage-variation cases. Critical coverage includes every random byte at all five reachable stages, Focus Energy, Scope Lens and the species-specific items. Accuracy coverage includes all stage pairs, Foresight, BrightPowder, perfect accuracy, X Accuracy, rain/Thunder, Dream Eater, drain/substitute failure and Jump Kick miss damage. Damage coverage includes 0/1's no-draw path, rounding and 16-bit boundaries. Mutating each command's threshold or divisor makes its comparison fail.

These are isolated command comparisons using controlled Link RNG inputs, not a claim of Link battle support or matching the hardware-timed non-Link RNG. Protect's text path and the refused Lock-On/Fly/Dig paths are outside these fixtures. Capture decision comparisons are described below; whole-battle reference comparisons remain open.

Validation

npm test
npm run test:e2e
npm run check:reference
npm run check:vendor
npm run build
npm run check:release
npm run build:reference

User-ROM tests skip when the file is absent, including public CI. Synthetic tests still run. Comparing with rebuilt graphics also needs the private PRET build. Do not report skipped private checks as CI passes.

Native production is dist/; the optional reference output is dist-reference/. Release checks reject emulator dependencies, binary game files and embedded binary assets in the native output. Source review is still required when adding assets or data.

Save schema

Native saves are version 3. Version 2 added scene values by owning map, phone contacts, the weekday offset and DST flag, and positions of objects that scripts moved on the current map. Version 3 adds the player ID, party, bag, Pokédex seen/caught sets and money. Early version-3 backups without money receive the original starting balance; explicitly invalid balances are rejected. Restores recompute each Pokémon's stats from its DVs and reject any mismatch, and check every item against its ROM pocket. Older saves migrate with new-game defaults; a missing player ID is drawn as a new game draws it. Objects are restored from the save on continue, and only the TILES callback runs, as in MapSetupScript_Continue.

Scripted trainer battle foundation

game/rom/trainers.ts decodes TrainerGroups, TrainerClassAttributes, TrainerClassNames, TrainerClassDVs and map trainer headers. Tests cover all 542 ROM records across 67 classes; CAL2 construction refuses its SRAM-dependent Mystery Gift party.

game/battle/ai.ts translates AIChooseMove, AI_Redundant and the Basic, Setup, Types, Offensive, Opportunist, Aggressive, Cautious, Status and Risky layers. It preserves the original random tie selection, known redundancy quirks, HP thresholds, exclusions and the deterministic pre-variation damage estimate used by Aggressive and Risky. Smart runs only for move effects that have no AI_Smart_EffectHandlers entry (Normal Hit, Attack Down, Defense Down; enough for the first rival). Other effects are refused before any random draw. Synthetic scoring vectors establish the tested branches; original-engine AI execution parity is still pending.

loadtrainer, winlosstext and startbattle run scripted trainer battles through the existing battle UI. Tests cover Joey's ROM party/text/reward, RUN refusal, trainer experience, Amulet Coin, CANLOSE behavior, money limits, transactional rollback and midbattle restore. Chromium and WebKit exercise the UI with a test-only script.

Map trainers

home/trainers.asm and engine/events/trainer_scripts.asm: talking to an OBJECTTYPE_TRAINER object runs TalkToTrainerScript with the object's header copied as wTempTrainer; _CheckTrainerBattle runs SeenByTrainerScript with wSeenTrainerDistance. The world checks sight in PlayerEvents order: before warps, coordinate events and encounters at the end of a step (a seen player's tile events are then skipped, as DisableEvents does), and on idle ticks before scene scripts and input. Walls and objects do not block sight. TrainerWalkToPlayer/ComputePathToWalkToPlayer build the raw wMovementBuffer bytes, which applymovementlasttalked decodes with the normal movement reader. wRunningTrainerBattleScript lives in the script run: zero at the start, set by loadmem after the battle so endifjustbattled ends the after-script. Trainer commands without a map trainer are refused. MomTriesToBuySomething after scripted battles does nothing while Mom's savings (not ported) are zero.

engine/battle/core.asm and engine/battle/ai/items.asm, switch.asm: when a trainer's Pokémon faints and others remain, UpdateBattleStateAndExperienceAfterEnemyFaint zeroes its party HP and runs NewEnemyMonStatus; EnemyPartyMonEntrance then sends out the Pokémon chosen by FindMonInOTPartyToSwitchIntoBattle. When every candidate is threatened it draws BattleRandom & 7, which tests pin. AI_SwitchOrTryItem runs before either side moves: CheckAbleToSwitch, the Often/Rarely/Sometimes thresholds, AI_TrySwitch and AI_Switch (withdraw text, HP and status back to the party). CheckTypeMatchup ignores the type its switch-AI callers load and uses BATTLE_VARS_MOVE_TYPE, so every such matchup uses the enemy's chosen move type; FindEnemyMonsWithASuperEffectiveMove never resets its result between Pokémon; FindEnemyMonsWithAtLeastQuarterMaxHP rotates HP bits instead of multiplying. All three bugs are kept. UsedMoveText records wPlayerUsedMoves. Refused: Pursuit on a switching Pokémon, Perish Song, Spikes, and trainer items. Side effects of the type scans on the move structs (overwritten types and animation) are not modelled; the next ParseEnemyAction/ParsePlayerAction reloads them.

BGEVENT_ITEM runs HiddenItemScript with wHiddenItemData; SetMemEvent sets the item's flag.

A trainer sighting whose script is refused is not restarted until the player moves. This is a native safeguard, not original behavior.

Next slice

Route 29, Cherrygrove, Route 30 and Mr. Pokémon's house are enabled with item balls, hidden items, fruit trees and the daily reset, the Pokémon Center nurse, the recorded whiteout spawn, map trainers, the first rival battle, Elm's special call, capture and the catching tutorial. NPCs roam. The PC and boxes are ported. Next: party, bag and Pokégear menus over the native models. Other specials stay refused until translated.

Reflect and Light Screen

BattleCommand_Screen in engine/battle/effect_commands.asm and HandleScreens in engine/battle/core.asm now run natively. Each screen has a side-owned five-turn counter, including its setup turn. Repeated use fails without refreshing it; send-outs preserve it. Expiration runs after defrost, before healing items, player before enemy and Light Screen before Reflect. Messages come from the ROM. The existing damage path doubles the appropriate defense and retains the original critical/stage rule. Safeguard and other screen flags remain refused. Seven local-ROM tests cover move execution, counters, PP, damage stats and send-out persistence; no screen-routine emulator parity or physical-device validation is claimed.

Mr. Pokémon, the first rival and special calls

MrPokemonsHouse.asm, CherrygroveRivalScene* and the ElmsLab.asm officer and Egg scripts run from the ROM. Supporting translations: blackoutmod, reloadmap (returns to the script; native presentation keeps the map), readvar VAR_SPECIALPHONECALL and memcall (only through wCallerContact + PHONE_CONTACT_SCRIPT2_BANK). Specials: NameRival (native naming field, ROM title and InitName default), FadeOutMusic, and the presentation-only fades. CountStep's CheckSpecialPhoneCall reads the queued SpecialPhoneCallList entry. It checks SpecialCallOnlyWhenOutside or SpecialCallWhereverYouAre, then runs CheckSpecialPhoneCall.script with that entry's caller script. RingTwice_StartCall and InitCallReceiveDelay are accepted without effect, because ringing presentation and random calls are not ported. HangUp shows "Click!" for its 140 frames. Local-ROM tests cover the house, both rival triggers with all three parties, a rival loss, the call indoors, outdoors and on reload, the officer's naming (including blank names and reload at the naming screen), and the Egg and Poké Ball handovers. Browser tests cover the house, the rival battle and the naming field.

Capture and the catching tutorial

PokeBallEffect, BallMultiplierFunctionTable (Poké, Great, Ultra and Master Balls), GetPokeBallWobble with WobbleProbabilities, UseBallInTrainerBattle and BattleMenu_Pack's .UseItem in engine/items/item_effects.asm, engine/battle_anims/pokeball_wobble.asm and engine/battle/core.asm. The catch rate is computed with the original 8- and 16-bit arithmetic and kept bugs (no bonus for BRN/PSN/PAR, overflow above 341 maximum HP). Only the random draws are kept from the throw animation: one per shake until the ball clicks or the Pokémon breaks free. The caught Pokémon follows the second LoadEnemyMon (the wild item roll is redrawn and then restored), GeneratePartyMonStats with wBattleMode set (wild moves, PP and HP) and SetCaughtData. Pokédex registration, NewDexDataText, AskGiveNicknameText and the naming field with InitName's default follow. The ball is taken from the selected slot, as RemoveItemFromPocket does with wCurItemQuantity.

Script_catchtutorial and CatchTutorial run the battle as BATTLETYPE_TUTORIAL: <PLAYER> reads "DUDE" from the ROM, DoBattle skips the send-out, and the auto input's PACK and ball choice go straight to PokeBallEffect, which always catches and keeps nothing (.FinishTutorial). Prompts continue on their own. The Dude's back picture, the ball animation, capture music and the Pokédex page (NewPokedexEntry) are not presented. TX_LOW text is now read as a line break.

Refused: the other ball multipliers, Park/Safari Balls, a transformed target and a catch-rate division by zero. Pure vectors cover the catch formula; local-ROM tests cover capture, every break-free message, Master Ball draws, blank nicknames, the blocked trainer ball, full-party rollback, both tutorial triggers, declining and the repeat offer, and mid-battle reloads. Browser tests cover PACK, catching and naming.

tests/reference-capture.spec.ts compares the production capture decision and shake loop with PokeBallEffect's calculation and the original GetPokeBallWobble. Each browser runs 3,220 capture cases and 7,424 shake cases: every catch-rate byte and supported multiplier, HP scaling and wrapping, status bonuses, success-draw equality, every random byte at each wobble-table entry, early/later escapes, and the Master Ball/tutorial bypasses. Final rates, outcomes, shake counts and random-draw counts match. The native decision and shake loop are private helpers called by the actual ball-use path; existing capture integration tests still exercise that path.

Unlike the battle commands, capture calls hardware Random. This fixture patches its entry in the private in-page ROM copy to consume supplied bytes, enters after the capture UI setup, and inserts a return after the decision. The catch arithmetic, ball multipliers and wobble routine are unmodified. It does not compare hardware RNG timing, animation, caught-mon reloading, party/PC writes, or a whole battle. No real held item has HELD_CATCH_CHANCE, so that synthetic effect remains covered by pure vectors only. Maximum HP 342 and 683 are omitted from emulator execution because their divisor is zero; synthetic tests verify the native refusal. Deliberate mutations of success equality, formula rounding and shake equality fail the comparisons.

Switching, battle items and the stats screen

engine/battle/core.asm: BattleMenu_PKMN and TryPlayerSwitch ("is already out", "can't be recalled" while wrapped or blocked by Mean Look, CheckIfCurPartyMonIsFitToFight with its fainted and Egg texts), PlayerSwitch and BattleMonEntrance. The switch runs ParseEnemyAction first, and ParsePlayerAction then skips it, so the random draws happen once. SendOutMonText and WithdrawMonText choose their cheer from the enemy's HP as a byte percentage of max HP / 4, including wEnemyHPAtTimeOfPlayerSwitch. A maximum HP below 4 would divide by zero and freeze the original; it is refused. PursuitSwitch reads the enemy move's effect as GetMoveEffect does, and Pursuit is refused.

After a faint, HandlePlayerMonFaint runs AskUseNextPokemon (wild battles only; NO tries to run, compared with the first party Pokémon's stored Speed) and ForcePlayerMonChoice, whose party menu cannot be cancelled. A double faint in a trainer battle goes through DoubleSwitch, and a fainted Pokémon gains no share of the experience. When a trainer sends out the next Pokémon, CheckWhetherToAskSwitch and OfferSwitch run Shift mode's offer (the only battle style, since options are not ported); switching clears both participant sets as the original does. NewBattleMonStatus also clears the enemy's wrap count and Mean Look.

engine/items/item_effects.asm and pack.asm: BattlePack shows the Items and Balls pockets. CheckItemContext gives Oak's "This isn't the time" text for items with no battle use. ItemEffects is read from the ROM and dispatches every non-ball effect usable in battle:

• Party items (.BattleField): RestoreHPEffect (ItemRestoreHP, HealingHPAmounts, RestoreHealth), StatusHealingEffect (UseStatusHealer, StatusHealingActions, HealStatus, IsItemUsedOnConfusedMon), FullRestoreEffect, ReviveEffect (half or full HP; a revived participant shares the experience again through wBattleParticipantsIncludingFainted), the bitter Energypowder, Energy Root, Heal Powder and Revival Herb (ChangeHappiness and "It looks bitter…"), BitterBerryEffect and RestorePPEffect (Ether, Max Ether, Elixer, Max Elixer, MysteryBerry; GetMaxPPOfMove, BattleRestorePP, a move prompt for MoveSelectionScreen whose B reopens the party menu).
• Battle-only items (.BattleOnly): XItemEffect (XItemStats, RaiseStat with hBattleTurn on the player, used even when the stat cannot rise, and the X-item happiness gain), X Accuracy, Guard Spec and Dire Hit (set once; a second use keeps the item), and PokeDollEffect (ends a wild battle as a draw; Oak's warning in a trainer battle).

"Won't have any effect" and a cancelled menu keep the item and the turn. wItemEffectSucceeded shares wBattlePlayerAction's byte, so a used item takes the turn. UseItemText waits for a button. ChangeHappiness reads HappinessChanges and updates the battle Pokémon's copy only when wCurPartyMon equals the 1-based wPartyMenuCursor, as in the original; fainting and levelling up use it too, and LevelUpHappinessMod gives the larger gain on the map where the Pokémon was caught.

CalcPlayerStats reapplies the paralysis and burn penalties to the side named by hBattleTurn after a switch of turns, which can be the enemy. hBattleTurn at the battle menu is modelled: DoBattle leaves the player's turn, HandleHealingItems ends a full turn on the enemy's, and the trainer AI reports when AI_Types, AI_Status or AIDamageCalc set it. A status heal after a full turn therefore penalises a paralysed or burned enemy again, as the original does. Remaining gaps: the special Kurt and Park balls.

engine/pokemon/stats_screen.asm: the stats screen's three pages (HP, status, types, experience to the next level; item and moves with PP; ID, OT and stats) with the ROM's strings, TypeNames, GetGender and the front picture. It opens from BattleMonMenu (B returns to the party menu, as BattleMenuPKMN_ReturnFromStats does) and from Bill's PC, where a boxed Pokémon shows CalcTempmonStats' full HP and no status.

Tests: local-ROM battles cover switching, cancelling, the withdrawal texts, forced choices (including a fainted pick and a cancelled forced menu), run after NO, Shift mode's offer (accepted and declined), a trainer double faint, and every item effect above, including the reapplied enemy penalty and the caught-location level-up bonus. Trainer AI tests pin its hBattleTurn reporting. The reference suite runs the original SendOutMonText (its final jump to BattleTextbox patched to ret in the test's ROM copy), WithdrawMonText's text routine, RestoreHealth, RestorePP, ChangeHappiness and CalcPlayerStats with both values of hBattleTurn: 300, 300, 200, 300 and 200 cases. Browser tests switch through the party menu, use a Potion from the Items pocket and page through the stats screen. WithdrawMonText still assumes the leftover multiplicand high byte is zero; a whole battle has not been compared with the original.

Start menu, party menu and pack

StartMenu.SetUpMenuItems builds the list from the Pokédex and Pokégear engine flags and the party, and StartMenu.Items supplies each item's string and description. The start menu runs as StartMenuRun, a native generator on a copy of the script state, so nothing commits before it closes and a save meanwhile keeps the previous state. POKéDEX, POKéGEAR, the trainer card and OPTION are not ported and give a notice.

The party menu prints PartyMenuStrings for the PARTYMENUACTION_* in use. GetMonSubmenuItems reads MonMenuOptions: field moves first, then STATS, SWITCH, MOVE, ITEM (MAIL when MailItems holds the held item) and CANCEL when fewer than NUM_MONMENU_ITEMS are listed; the strings come from MonMenuOptionStrings and move names. SwitchPartyMons/_SwitchPartyMons swap two party entries. MoveScreenLoop swaps two moves and their PP; the original's flag-dependent write into wBattleMon after a swap outside battle is not modelled (the next battle reloads that structure), and left and right do not move to another Pokémon's moves. GiveTakePartyMonItem, TryGiveItemToPartymon (including the swap and the full-pack refund) and TakePartyItem use GiveItemToPokemon/ReceiveItemFromPokemon on the chosen pack slot. Giving MAIL needs ComposeMailMessage and is refused before anything changes.

The pack's submenu follows .ItemBallsKey_LoadSubmenu: CANT_TOSS, CANT_SELECT and the field menu (CheckItemMenu, the help byte's high nibble) pick one of the six MenuHeader_* menus. TossMenu confirms the quantity and tosses from the chosen slot. UseItem dispatches by field menu and then _DoItemEffect by the ItemEffects routine address, with the field side of RestoreHPEffect, StatusHealingEffect, FullRestoreEffect, ReviveEffect/RevivalHerbEffect, EnergypowderEffect/EnergyRootEffect, HealPowderEffect and RestorePPEffect (Ether, Max Ether, Elixer, Max Elixer, MysteryBerry and PP Up with ApplyPPUp). Items are used from the Items pocket slot they were chosen from (wCurItemQuantity). ItemActionTextWaitButton prints PrintPartyMenuActionText with the HP change. ChangeHappiness outside battle does not touch a battle Pokémon. BicycleEffect runs BikeFunction's checks; a queued script runs once the menu closes, and a refusal gives Oak's warning because wFieldMoveSucceeded and wItemEffectSucceeded share a byte.

wBattleMenuCursorPosition, wPartyMenuCursor and wLastPocket persist between openings in memory and are cleared when a battle ends (CleanUpBattleRAM). The party cursor is passed to the next battle, whose ChangeHappiness compares it with wCurPartyMon.

Tests: tests/start-menu.test.ts (local ROM) covers the item list and descriptions, the cursor, the submenu with field moves, switching, move reordering, giving, swapping and taking items (including a full pack and MAIL), every ported field effect, the PP Up step and its maxed-out refusal, tossing, the Bicycle outdoors and indoors, unported effects and saving while the menu is open. A Chromium/WebKit test opens the menu with Start, switches Pokémon, changes pockets and tosses a Potion. These are not emulator comparisons.

Evolution

The battle's experience routine sets a party member's bit in wEvolvableFlags when it levels up. ExitBattle runs EvolveAfterBattle only when wBattleResult & $0f is a win; the world then presents it before the script receives the battle result, on the same draft, so the evolution commits with the battle. CleanUpBattleRAM's cursor reset follows.

EvolveAfterBattle reads EvosAttacksPointers and walks each Pokémon's entries with the original's pointer steps (.dont_evolve_1/2/3): trades are skipped without Link, a forced evolution (a stone) skips every non-item entry by two bytes, items need wCurItem and wForceEvolution, levels and happiness (HAPPINESS_TO_EVOLVE, TR_* against wTimeOfDay) and Tyrogue's EVOLVE_STAT check the copied Pokémon, and an Everstone blocks all but items. The first match evolves; a stopped evolution goes on to the next Pokémon. UpdateSpeciesNameIfNotNicknamed compares the nickname with the old species' name (wBaseDexNo, which the animation restores). CalcMonStats uses the stat experience; HP rises by the maximum HP's increase. LearnLevelMoves then offers moves at exactly the current level, and SetSeenAndCaughtMon records the species.

EvolutionAnimation is presented as a picture schedule in overworld ticks: 40 ticks on the old picture, then seven rounds of a B-checking wait (7 … 1 ticks) and that many flashes (two ticks each way). The waits and flashes are approximations of the original frame timing; B is accepted only during the waits and never when wForceEvolution is set. No music, cry, palette or AnimateFrontpic is presented.

LearnMove outside battle: the first empty slot, otherwise ForgetMove (yes/no, then a move list; IsHMMove refuses HM moves), Text_1_2_and_Poof with its text_asm continuation, or "Stop learning" (NO asks again) and "did not learn".

PACK items: RareCandyEffect (CalcExpAtLevel for the new level, the HP rise that also revives a fainted Pokémon, LevelUpHappinessMod against the caught landmark, PARTYMENUTEXT_LEVEL_UP, a PrintTempMonStats page, LearnLevelMoves and an unforced EvolvePokemon), EvoStoneEffect (PARTYMENUACTION_EVO_STONE's ABLE/NOT ABLE labels copy ten bytes and step three at a time, as the original does; bytes past the copy read as the end here, where the original reads stale RAM) and VitaminEffect (StatExpItemPointerOffsets, the high byte limit of 100, StatStrings, ItemStatRoseText and HAPPINESS_USEDITEM).

Tests: tests/start-menu.test.ts covers the Rare Candy level-up, stat page, HM refusal, forgetting and declining a move, the revived fainted Pokémon, evolution with and without B, a stone (ABLE labels, no effect on another species or with an Everstone, B ignored, a kept nickname) and a vitamin up to its limit. tests/battle-world.test.ts wins a wild battle whose level-up evolves Cyndaquil, and checks that a non-participant that could evolve does not. A Chromium/WebKit test evolves through a Rare Candy. No emulator comparison of these routines yet.