The Secret of Monkey Island on the STM32F429I-Discovery

The Secret of Monkey Island, running completely on the STM32F429I-Discovery board: the SCUMM engine of ScummVM, ported to the Cortex-M4 with FreeRTOS, in landscape mode on the 2.4 inch display, controlled via touch, with AdLib music through the DAC. The game data comes from your own copy of the game (VGA floppy version) on a USB stick.

Status: playable. Intro, rooms, menus and music work; room changes without audio dropouts.

Photos, a video and the background story: palm2000.com

No game data included. The Secret of Monkey Island is © Lucasfilm Games / Disney. This repository contains only the engine port and the board support code. You need your own copy of the game, exactly like with ScummVM on a PC.

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Controls

Hold the board in landscape orientation, with the ST-LINK connector on the left.

Input	Action
Tap	Left click at this position (verbs, items, walking)
Drag	The mouse pointer follows the finger
USER button (blue), short	Escape: skip a cutscene
USER button, long (0.8 s)	ScummVM menu: save, load, options
RESET button (black)	Restart; the loader loads the game from the stick again

Saved games are stored on the stick in /SAVES, the settings in /SCUMMVM.INI.

Hardware

	STM32F429I-Discovery (MB1075)
CPU	STM32F429ZI, Cortex-M4F, 168 MHz (USB needs 48 MHz from the PLL)
Memory	2 MB flash, 192 KB SRAM + 64 KB CCM, 8 MB SDRAM (FMC bank 2, 0xD0000000)
Display	2.4 inch, 240×320 portrait, ILI9341 on the LTDC
Touch	resistive, STMPE811 on I²C3
USB	USB ST-LINK (Mini-USB, top): power, flashing, debugging · USB USER (Micro-USB OTG, bottom): USB stick

USB stick (FAT32, root directory)

File	Content
000.LFL, 901.LFL … 904.LFL	Game files from your own copy (VGA floppy version)
DISK01.LEC … DISK04.LEC	Game files from your own copy (VGA floppy version)
MONKEY.BIN	The game program (firmware/build/MONKEY.BIN)

The ._* files that macOS creates on FAT sticks do no harm; the file system hides dot files.

Audio output (line level on PA5)

The sound comes from DAC channel 2 on PA5 (lower pin header P1, inner pin directly above the "PA4" label). For active speakers:

 PA5 --- 100 Ohm --- (+) 10 uF (-) --+----------+---- jack tip    (left)
                                     |          +---- jack ring   (right)
                                   10 kOhm
                                     |
 GND --------------------------------+--------------- jack sleeve

The 100 Ω resistor limits the level so the speakers are not overdriven. The capacitor blocks the DC voltage (the DAC rests at about 1.45 V), and the 10 kΩ resistor keeps the output at ground level (no crackling when plugging in). The DAC output is designed for loads of 5 kΩ and more; headphones work, but they are quiet.

Architecture

 Flash (0x08000000)          SDRAM (0xD0000000, 8 MB)              SRAM (0x20000000, 192 KB)
 ┌──────────────┐            ┌─────────────────────────┐           ┌─────────────────────────┐
 │ Loader 29 KB │ ──loads──▶ │ Frame buffers L8+RGB565 │           │ Audio code + OPL tables │
 └──────────────┘            │ MONKEY.BIN (2.7 MB)     │ ─copies─▶ │ Vector table, log       │
                             │   ScummVM + backend     │           │ Task stacks (96 + 12 KB)│
                             │ Heap up to the end      │           │ Interrupt stack         │
                             └─────────────────────────┘           └─────────────────────────┘

• Loader in flash (firmware/loader): starts clock, SDRAM, MPU, USB host and FatFs, loads MONKEY.BIN from the stick to 0xD0040000 and jumps into it. Display: blue = waiting for the stick, green bar = loading, red = error (see below).
• Code in SDRAM. ScummVM with the SCUMM engine is larger than the flash. On the Cortex-M4, the range 0xC0000000–0xDFFFFFFF is "device" memory and not executable; an MPU region turns the 8 MB into normal, executable memory. (Remapping via SYSCFG_MEMRMP.SWP_FMC does not work on this board: bank 2 does not show up anywhere afterwards.)
• Hot path in SRAM. The SDRAM has no cache and is 16 bits wide. The AdLib emulation (DOSBox OPL), the mixer and the rate converter therefore live in .ram_text/.ram_bss and are copied to SRAM before the constructors run (.preinit_array).
• FreeRTOS (game/FreeRTOSConfig.h): ScummVM runs as one task, the mixer in its own task with higher priority, woken by the DMA interrupt of the audio output. ScummVM mutexes are recursive FreeRTOS mutexes with priority inheritance, so loading a room (ScummVM holds the resource mutex for up to 400 ms) does not stall the audio. The HAL time base runs on TIM7; FreeRTOS owns the SysTick.
• Display (scummvm/ltdc-graphics.*): the game picture (320×200, 256 colours) is rotated by 90° into an L8 layer (4×4 blocks, transposed in registers); the VGA palette lives in the LTDC colour lookup table. ScummVM's menus draw into a second layer (RGB565, 320×240). Screen shaking only moves the layer window.
• Audio (board/audio.*, scummvm/stm32-mixer.*): DAC2 on PA5, TIM6 as sample clock, double-buffered DMA, 11025 Hz mono. The emulation needs about 35 % of the CPU; at 22050 Hz it was around 70 %.
• Files (scummvm/fatfs-fs.*): ScummVM file system on top of FatFs; writes (saved games) are atomic via .tmp and rename.

Building

Requirements: Arm GNU Toolchain 15.3 (firmware/Makefile, variable TOOLCHAIN), stlink, OpenOCD.

git clone --recurse-submodules https://github.com/User7142/scummvm-stm32.git
cd scummvm-stm32/firmware
make                 # configures and builds ScummVM (takes a while the first time), loader, MONKEY.BIN
make flash           # writes the loader to the flash
cp -X build/MONKEY.BIN /Volumes/<stick>/

Further targets: make bringup / make flash-bringup builds the bring-up program (SDRAM test, colour pattern, touch point, 440 Hz test tone when touched).

Development without copying to the stick

tools/run-game.sh    # load MONKEY.BIN into SDRAM via ST-LINK and start it (~30 s)
tools/read-log.sh    # game log (ring buffer in SRAM): ScummVM messages,
                     # audio load every 10 s, underruns, free stack, heap
tools/read-fault.sh  # decode the last processor fault (frame, CFSR …)

Error codes (red LED blinks n times)

n	Meaning
2	Loader: no USB stick detected
3	Display or FreeRTOS assert (details in the log)
4	Loader: MONKEY.BIN missing or unreadable · Game: touch controller does not respond
5	Loader: MONKEY.BIN is not a valid program · Game: stack overflow
6–9	Processor fault (usage, bus, MemManage, HardFault) → tools/read-fault.sh

Known limits

• No battery-backed clock: all saved games carry the same date.
• Music only via AdLib. A real MT-32 could be connected via a UART MIDI output (not built); the Cortex-M4 cannot emulate one.

Libraries (Git submodules, shallow, fixed releases)

Path	Source	Version
lib/scummvm	scummvm/scummvm	v2026.3.0
lib/freertos	FreeRTOS/FreeRTOS-Kernel	V11.3.1
lib/stm32f4xx_hal_driver	STMicroelectronics	v1.8.5
lib/cmsis_core, lib/cmsis_device_f4	STMicroelectronics	v5.9.0_20250520, v2.6.11
lib/usb_host	stm32_mw_usb_host	v3.5.5
lib/fatfs	stm32_mw_fatfs	r0.16_stm32cube_20260904

The board drivers (display, touch, SDRAM, audio) are small drivers of their own on top of the HAL (firmware/board); the hardware values come from the ST BSP.

License

ScummVM is licensed under the GNU GPL v3, and so is this port (see LICENSE). FreeRTOS is licensed under the MIT license; the ST libraries under their respective licenses.

The Secret of Monkey Island is © Lucasfilm Games / Disney. This is a private fan project; no game data is included.