01 / HOSTSupported
Bare metal
ESP32-S3
A real handheld: 8 MiB flash, 8 MiB PSRAM, an 800 × 480 RGB panel and GT911 touch. LVGL renders the same UI tree the browser does.
- ESP-IDF + FreeRTOS
- LVGL 9.5
- TF card apps
Platforms · three hosts
Three hosts.
One binary.
The same compiled app, the same runtime, three different machines. Hosts own the window, the event loop and the pixels; the app contract stays identical.
Pick a screen
Each host implements the same narrow port. They differ in platform services, not in app semantics.
02 / HOSTSupported
Desktop
macOS
SDL3 owns the window and event loop; the shared Rust runtime executes MBC and LVGL paints it. Apple Silicon is the tested target.
- SDL3 + LVGL
- Native HTTP + dictionary
- Double-clickable bundle
03 / HOSTSupported
Browser
Web
The same runtime compiled to WebAssembly, rendering DOM instead of LVGL. No JavaScript app runtime and no embedded JS engine.
- Wasm + DOM
- Desktop + mobile
- Device simulator
Windows / Linux native is source-level groundwork; iOS / Android are out of scopeSee the matrix
The reference device
An ESP32-S3 Touch LCD 7: enough flash, PSRAM and pixels to run a real app contract.
| SoC | ESP32-S3 · 8 MiB flash · 8 MiB PSRAM |
| Display | 800 × 480 RGB565 · 16 MHz |
| Touch | GT911 capacitive controller |
| Expander | CH422G · reset / backlight / SD chip select |
| Storage | TF card over SPI · MOSI 11 · MISO 13 · SCLK 12 · CS EXIO4 |
| Input | BOOT button on GPIO0 · edge-swipe back gesture |
| Console | UART0 · 115200 baud |
| Partitions | factory app 0x10000 / 0x3D0000 · micro_app 0x3F0000 / 0x3F0000 |
| Kernel | ESP-IDF 5.5 + FreeRTOS (owned by the platform) |
The board is a host, not a target abstraction. The runtime does not know it is on a microcontroller: it receives a UI tree and a render patch, and the LVGL adapter paints it.
A missing TF card is a warning, not a boot failure. Without a card, storage.available() is false,/apps is ignored, and the built-in apps still launch.
The wall clock is SNTP-backed through micro_clock; before the first sync, clock.now() falls back to uptime.
Boot chain
Ten steps from power to a running shell. No JS engine, no parser, no package manager.
Verify the board
8 MiB flash / 8 MiB PSRAM class check; abort on mismatch.
Bring up the panel
RGB LCD, GT911 touch and CH422G expander; enable the backlight.
Mount the card
A missing TF card warns; it does not stop boot. storage.available() reports it.
Smoke / health screen
Draw, mark the board profile healthy, clear for the shell.
Start platform services
BOOT button, Wi-Fi STA, KV, SNTP clock, OS reducer.
Dispatch boot events
BOOT_SAMPLED … SETUP_SKIPPED; first-run setup is skipped in this slice.
Scan built-in apps
Raw micro_app partition, up to 8 manifests beside the shell.
Scan the SD card
Top-level /apps/*.mbc, malformed images skipped, built-in ids win collisions.
Load the shell
Destroy any previous runtime, load shell.mbc into PSRAM, create its Runtime.
Start the tick
Install the host app bar; create the 30 ms LVGL timer that drives the runtime.
Support matrix
What is tested, what is groundwork, and what is deliberately out of scope.
| Target | Status | Notes |
|---|---|---|
| macOS native (SDL/LVGL) | Supported | Apple Silicon is the tested target. |
| Web browser (Wasm/DOM) | Supported | Desktop and mobile, with a responsive simulator. |
| ESP32-S3 reference board | Supported | 800 × 480 RGB panel, 8 MiB flash + 8 MiB PSRAM. |
| Windows / Linux native | Groundwork | Portable SDL layer exists; no packaged launcher, not verified on real desktops. |
| Native iOS / Android | Out of scope | No host or packaging layer. Mobile browser access works through the Web Player. |
One honest caveat.
The browser simulator executes the shared runtime and the OS reducer, but it does not emulate ESP-IDF, RGB timing, GT911 electrical I2C, PSRAM allocation, the Wi-Fi radio or physical hardware success.
The browser simulator executes the shared runtime and the OS reducer, but it does not emulate ESP-IDF, RGB timing, GT911 electrical I2C, PSRAM allocation, the Wi-Fi radio or physical hardware success.