Android (USB)

USB-serial runs in Rust: the android-usb-serial crate (a port of usb-serial-for-android on top of nusb). Kotlin only asks for USB permission and hands over the device file descriptor.

Supported chips: FTDI (FT232R, FT2232, FT4232, FT232H, FT-X), Silicon Labs CP210x (CP2102/2104/2105/2108), Prolific PL2303 (all types incl. HXN/GC/GS/GT), WCH CH340/CH341, Chrome OS CCD, Unisoc GSM modems, and any CDC-ACM device (Arduino, RP2040, STM32 VCP, ESP32-S2/S3 native USB, CH9102, CH343, modems).

Nothing to configure in the app:

• The plugin adds a USB_DEVICE_ATTACHED intent filter for those devices to your activity, so Android offers to open the app when one is plugged in.
• open() asks the user for USB permission the first time.
• available_ports() lists attached devices. Paths are the USB device name (/dev/bus/usb/001/002); multi-port chips get one path per port (/dev/bus/usb/001/002#0, …#1).
• bytesToWrite() is always 0 (writes complete synchronously).
• A chip that answers a control request with a short packet gives an error on that call (e.g. readClearToSend()), not a crash.

Bluetooth LE serial (ble://, feature ble) works on Android too, see Bluetooth LE for its permissions (added to the app manifest only with ble).

The Android emulator has no USB passthrough; test with a phone, or use tcp:// to a bridge on the host (the emulator reaches the host as 10.0.2.2).