Entry 15

How the game is put together: boot, modes, frames and tasks

2026-09-22enginedecomp

Filesdocs/engine/overview.md

The top of the program, read from main down. A port needs this shape before any subsystem; the summary is on the overview page.

Boot

main (INF SLUS_202.67:0x0015a780, main.cpp) calls, in order, ccHeap::InitFirst, mwInit, ccCdInit, InitCCSys, ccLoad_SndModules, ccSndInit, ccMcardInit and ccInitThread, starts two tasks - ccPadThread and ccThMother - and then loops forever: WakeupThread on the control task tscbCtrl, SleepThread, ccSystem::Ctrl, ccAddPlayTime.

ccThMother (0x00167940, mother.cpp) builds the long-lived systems: the common file list and resources (ccSetFileListCmn, ccLoadResourceFL), the fonts, the sound task ccSoundMain, the gcmn file list, the draw packet controller and layer, the screen fader, ccGame (global game), ccSaveSys, ccSaveData (global saveData), ccEvent (global eventMng) and the event task ccThEvent. It starts event 1 and asks for mode 2 with ccGame::ChangeRequest(2, 7).

Modes and overlays

ccGame.request[4] is a queue. Each time round, ccThMother takes request[0], shifts the rest down, and dispatches:

Each setup tears down the previous mode (ccDeleteAllThread, ccDrawEnv::Reset, font and layer flips), loads its overlay, sets its file list and loads its resources. The overlay is loaded on a task, ccThLoadOverlay (0x001680e0), which calls mwLoadOverlay (4) with a path from overlay_tbl and retries until it returns non-zero. Paths are cdrom0:\DATA\DEMO.PRG, DESKTOP.PRG, TOPPAGE.PRG, GCMN.PRG. ccSetupGameCtrl picks the town, field or dungeon file list (ccSetFileListTown/Field/Dungeon) and starts the field game. ccLoadOverlay (0x00168030) can also be called from four places in the event script interpreter ccEvent::Execute - a function large enough that those calls are at offsets 0x7650 to 0x76a4.

Main calls straight into gcmn at fixed addresses - ccSetupNewGame calls ccSPC::Initialise and ccParty::InitParty, ccSetupGameCtrl calls ccStoreSpcCondition and initHitCheck, all in gcmn - so those paths are only valid while gcmn is the resident overlay. The relocations record these cross-overlay calls like any other.

Frames

ccSystem::Ctrl (0x0010a5f0) is one frame: shadow packets, wait for the GS path (sceGsSyncPath), then wait for vertical sync until frameRateCnt >= frameRate; reset the count, zero EE Timer 0 (a store to 0x10000000), bump ccSystem.count, set the screen mode, flush the cache, swap the double buffer, queue the font and layer display lists, SendDMA, read both pads, refresh the display list. VSyncCallBack (0x001099e0) increments frameRateCnt and a global tick every vertical blank.

So frameRate is vertical blanks per frame: 1 is 60 frames per second on NTSC, 2 is 30. SetFrameRate is called with 1 by ccSystem::Init, ccThMother, and the demo, desktop and bulletin-board setups; with 2 by ccSetupNewGame; and by the event interpreter (once with 2, once with a computed value). The field game runs at 30 frames per second, the desktop at 60. That matches the 30 fps inferred for the cutscenes in 14.

Tasks

Every task is a PS2 kernel thread wrapped in a ccTscb (0x54 bytes: entry, tid, priority, sleep, sr start request, del delete stage, mask flags, eight params, link, name, two cleanup callbacks, stack). ccStartThread allocates one and ccTscb::GoThread (0x00159d40) does CreateThread + StartThread with the game's $gp.

Scheduling is cooperative and frame-locked. Once per frame main wakes the control task ccThControl (0x0015a5c0), which walks the ccTscb list: a pending start request gets StartThread; a task being deleted runs its funcI callback at stage 2 and is terminated, deleted and freed at stage 3; a suspended task (mask bit 0x08) is resumed; and a task that is waiting in Breath (mask bit 0x20) and not held by its sleep flag gets WakeupThread. ccTscb::Breath(n) (0x00159e10) sleeps through n of those wake-ups and then keeps sleeping while sleep or del is set. A task's per-frame work is the code between two Breath calls; the kernel's thread priorities decide the order tasks run in within a frame, then main resumes and draws.