Dungeon Master II Skullkeep FM Towns — technical guide

Current Firestaff status

Firestaff admits the authentic FM Towns route from the original HME-242 ZIP, reads its disc image in memory and retains the archive as the source owner. The native M11 route reaches a bounded New Game/runtime handoff through source-owned inventory, movement, pit, stairs, DB1 and creature/THINK_CREATURE checks. This is a verified start route, not a claim that the original palette, title/menu timing, HUD or dungeon presentation is fully matched.

The Japanese FM Towns disc remains the owner of dungeon, graphics, title and animation media. Firestaff supplies selected-language text through its own localisation catalogs; it does not require a PC-English GRAPHICS.DAT companion. No archive member is unpacked as a substitute runtime tree.

DM2’s FM Towns port sits alongside DM1 and CSB in the Fujitsu HMA-240 Phar Lap family. Read this together with the DM1 and CSB FM Towns guides plus docs/fmtowns/CROSS_GAME_COVERAGE.md.

Retail media

Disc archive: Dungeon-Master-II-Skullkeep_FM-Towns_JA.zip (Victor Entertainment, 1993). Track 01 is a MODE1/2352 image; strip 288-byte-per-sector CD headers to get the 2048-byte ISO stream.

Byte-verified file inventory:

Full manifest in docs/fmtowns/all_games_real_data_hashes.json.

Phar Lap P3 layout

SKULL.EXP: level-1 header, load offset 0x200, init EIP 0x5741c, no SYM1 table (stripped from release). TWANIM.EXP is the animation binary: load offset 0x200, init EIP 0x10470.

Phar Lap real-mode bridge

Same 4-slot layout as DM1 and CSB (fmtowns_pharlap_all_games):

Direct hardware I/O

SKULL.EXP touches ONLY port 0x04E9 (SOUND_INT_REASON, one read), consistent with DM1 EDM.EXP and CSB CHTWE.EXP. TWANIM.EXP same. Verified via fmtowns_direct_io_cross_game_profiles.

Byte-verified DM1↔DM2 shared payloads

DM2 shares less with DM1 than CSB does (different game mechanics, different asset atlas). Confirmed shared:

DM2 does NOT share DYNA_BUTTONS labels (Skullkeep has different action set — no BLOCK/CHOP/FIREBALL/FUSE strings in SKULL.EXP) or OICON descriptors (different item/thing set).

GRAPHICS.DAT format — extended v4

DATA/GRAPHICS.DAT starts with signature 0x8004 (extended format v4). The authenticated FM Towns file is 2,783,791 bytes and contains 3,407 raw items. Its verified container layout is:

[u16 sig=0x8004] [u16 count=3407] [u32 raw[0] size] [u16 raw[1..3406] size] [raw[0] payload] [raw[1] payload] …

The size table begins at offset 4. Raw item 0 begins at 6 + 2 * count and is an ENT1 directory; subsequent raw-item offsets are the cumulative sizes from that table. The authenticated walker is dm2_v1_fmtowns_graphics_dat_ext_walker and verifies that the stored raw payload sum equals the file payload span. It does not reinterpret the raw items as {size, flags} records.

The source-specific IMG2/U4 decoder currently consumes the real hand-action fields in INTERFACE_GENERAL. The production route is covered for all 64 valid source tuples (two possession slots, two left/right entries, four party positions and four facings) by dm2_v1_gdat_image_helper_receipts against the authentic Towns v4 file. The runtime now carries the source-owned party.curacthero and party.curactmode values through GAME_LOAD and binds the selected champion’s authentic Towns action image only when those fields identify a valid selection. The selected hand now follows the source c_hero record link through the authenticated record pools, resolves its real class and command text, and draws its real item image. For commands with CnNC 16, 17, 18, or another positive charge requirement, the runtime reads the authentic record w2 through the exact ADD_ITEM_CHARGE(object, 0) semantics and admits the image only when the source charge is sufficient. DB9 containers with ContainerType()==0 follow the separate source admission branch for IS_CONTAINER_MONEYBOX/IS_CONTAINER_CHEST; the CONTAINERS/cls2/dtText/0x40 GDAT entry is queried from the original file to distinguish the moneybox list, and no command-entry or charge probe is substituted for that branch. The charge probe uses a local w2 copy and never mutates the mounted record pool. The hand cooldown byte and the source sleep/wake input drive the authentic checker-pattern overlay. Unknown items remain unavailable rather than becoming a generated surface.

The native FM Towns HUD route also binds every authentic CHAMPIONS type 0..15 through the M11 portrait-plan owner. This is covered by test_dm2_v1_fmtowns_hud_portraits_real_data; it does not use the DOS companion graphics file as a portrait source.

After GAME_LOAD, the M11 champion-cycle input now advances the source-owned party.curacthero selection through occupied champions retained in the real session records. Empty or incomplete formations remain unavailable; Firestaff does not create a champion slot merely to make the key appear responsive.

What is NOT yet ported

• DM2 SKULL.EXP SYM1 symbol table (stripped from release binary).
• The complete FM Towns c_tmouse/c_input runtime dispatch. The authenticated boot profile now retains the original 264-record SKULL.EXP MOUSE_INPUT span (1584 bytes, FNV-1a 0x1500c4c9) and the input owner exposes its raw event/flag/rect/mask candidates with source ordinals. The M11 bridge still promotes only the verified movement, action-panel, and champion-hand subset through Towns INTERFACE_GENERAL RAW4 rectangles. It does not reuse the PC rectangle pool or promote an ambiguous candidate without a UI-context owner. The source-ordinal context bridge is now available to runtime owners, and event 0x70/112 closes the active hand/action panel through the M11 path. The inventory route census currently resolves 129/166 contexts to native RAW4 rectangles. Source ordinals 47-49, 52-83, 99, and 110 are retained as evidence but remain unavailable because no matching rectangle exists in the authenticated Towns RAW4 set. The M11 event bridge now admits source panel-close event 11 after native rectangle admission. Events 142/143 exist in the generic c_input callback contract but are not present in the authenticated 264-record Towns pointer span, so they are not exposed as pointer routes. Item-slot, rune, moneybox, and status mutations remain unavailable until the original record-chain owner is bound. For a source-complete GAME_LOAD session, the runtime inventory API now reads and writes the authentic c_hero::item[30] links and validates non-empty handles against the admitted record pool. This does not promote the real DOSBox SKSave corpus to resume: those files still stop at the verified pre-link GAME_LOAD boundary. The Towns v4 file’s raw item 201 is only 6 bytes (0f220d34fbfa, MD5 76490b63a215739e633bb168e58bf60387), not the PC-English rectangle pool (25247ede4dabb6a71e5dabdfbcd5907d). Inventory, dialogue, sensor/object, and complete viewport event ownership remain unavailable until their source UI-context mappings are recovered; rect IDs such as 0x003f are reused by multiple original input branches.
• Broader DM2 extended-v4 item-to-screen mapping beyond the authenticated ENT1 directory and hand-action IMG2/U4 fields.
• DM2 region table (different menu layout from DM1/CSB).
• DM2-specific game tables (DOOR_PAL, LEVEL_SONGS, DYNA_BUTTONS labels, OICON descriptors).
• FM Towns native SKSAVE resume/writeback. The local authentic FM Towns corpus contains no SKSAVE slot; DOS SKSAVE files are not substitutes.

What is shared with DM1/CSB

Everything under “Byte-verified DM1↔DM2 shared payloads” above, plus the Phar Lap bridge and TownsOS BIOS integration surface common to all three games. Consumers can use the shared cross-game modules (fmtowns_geometry_all_games, fmtowns_shared_tables_all_games, fmtowns_font_raster_all_games) to access DM2’s data through the same code that handles DM1 and CSB.