Shrinking the firmware
Dead .class debug attributes stripped from the device image, and the shrunk java/** classes moved under a short b/ namespace that the JVM un-shrinks on load. Measured together: 969,452 bytes down to 959,911.
Index · 01
picodroid
A stripped-down, FreeRTOS-based Android for the Raspberry Pi Pico. Java apps run on a JVM interpreter written in Rust, directly on bare-metal hardware.
[Photo of a Pico running a picodroid app]
Why
Android's app model is a good way to structure small interactive programs: activities with a lifecycle, a back stack, views, preferences, background threads. It also assumes a phone. picodroid asks how much of that model survives on a four-dollar microcontroller with a few hundred kilobytes of RAM.
The answer so far is: enough to write real apps in Java against an Android-compatible API, install them over USB without reflashing the firmware, and run them on both cores under FreeRTOS.
What runs today
- ActivitiesFull lifecycle with a back stack
- UILVGL-backed widgets: Toast, AlertDialog, Keyboard, gestures, property animations
- StorageFiles on LittleFS, SharedPreferences
- NetworkingTCP, UDP and HttpURLConnection over WiFi on the Pico 2 W
- SensorsSensorManager with a BME688 environmental sensor
- ThreadsThread.start() creates FreeRTOS tasks; concurrency utilities
- MemoryMark-sweep garbage collector, runs every 256 allocations
- ToolingHot-swap installs and a device monitor over USB, plus a desktop simulator with mouse-as-touch
Build log
First light: LED blink from a no_std binary
Where it started. Boots through cortex-m-rt into main, takes the peripherals, sets GPIO25 as a push-pull output and toggles it on a busy-wait delay. No RTOS, no JVM, no display.
let mut led = pins.gpio25.into_push_pull_output();
loop {
led.set_high().ok();
cortex_m::asm::delay(12_000_000);
led.set_low().ok();
cortex_m::asm::delay(12_000_000);
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