pixdr

pixdr is a pure-Rust Android NativeActivity SDR app for using an Ettus/NI USRP B210 from an Android phone over USB host mode.

Current target setup:

• Android NativeActivity, no Java/Kotlin app code
• Rust UI with egui/eframe/wgpu
• FutureSDR flowgraph backend with a custom UHD B210 source block
• UHD 4.10 built for Android arm64
• B200/B210 Android USB fd handoff flow inspired by GNU Radio's GrHardwareService
• B210 firmware/FPGA loading through UHD

Repository layout

pixdr/
  app/                    Rust NativeActivity app, AndroidManifest, assets, resources
  external/               External dependencies (git submodules in release)
    uhd/                  m4tsuri/uhd, branch pixdr-android-uhd-4.10
    libusb/               upstream libusb, tag v1.0.27
    uhd-rs/               m4tsuri/uhd-rust, branch pixdr-android
    boost-android/        m4tsuri/Boost-for-Android, branch pixdr-android
    FutureSDR/            FutureSDR runtime used for the receive flowgraph
  build/                  Generated native build/toolchain workspace (ignored)
  docs/                   Project notes and architecture notes
  patches/                format-patch exports of fork changes
  scripts/                Supported build/install/log entrypoints

Important app files:

• app/src/lib.rs — egui UI and B210 worker orchestration
• app/src/futuresdr_backend.rs — FutureSDR UHD source block and spectrum sink block
• app/src/usb.rs — Android USB permission and UsbDeviceConnection fd acquisition via JNI
• app/src/uhd_wrapper.rs — UHD init/open using injected Android USB context
• app/AndroidManifest.xml — NativeActivity declaration

Prerequisites

Host tools:

• Linux host
• Android SDK with platform 29+ and build-tools 35.x
• Android NDK r27d extracted to build/native/android-ndk-r27d or provided via PIXDR_NDK=/path/to/ndk
• Rust nightly + cargo-ndk
• cmake, make, wget, tar, zip, keytool
• adb

Install Rust pieces:

rustup target add aarch64-linux-android
cargo install cargo-ndk

Android SDK defaults to $HOME/Android/Sdk. Override with:

export ANDROID_HOME=/path/to/Android/Sdk

Checkout

git clone --recursive https://github.com/m4tsuri/pixdr.git
cd pixdr

If already cloned:

git submodule update --init --recursive

Build

1. Build native dependencies from scratch

This builds Boost, libusb, and UHD into build/native/toolchain/arm64-v8a:

scripts/build-native.sh

This step is slow and assumes external/ has been initialized with the pixdr fork branches plus upstream libusb.

2. Fetch B200/B210 runtime images

scripts/fetch-uhd-images.sh

This populates app/assets/ with the three files packaged into the APK. They are intentionally ignored by git until redistribution licensing is decided.

3. Build the APK

scripts/build-apk.sh

Output:

app/pixdr-debug.apk

4. Install and run

scripts/install-run.sh

5. Follow logs

scripts/logcat.sh

Fast rebuild during development

If native dependency build directories already exist:

scripts/rebuild-all.sh

This rebuilds native dependencies/UHD, builds the Rust app, packages the APK, installs it, and starts the app.

Environment overrides

All scripts source scripts/env.sh. Useful overrides:

export ANDROID_HOME=/path/to/Android/Sdk
export PIXDR_NDK=/path/to/android-ndk-r27d
export PIXDR_ANDROID_API=29
export PIXDR_PREFIX=/path/to/android/uhd/prefix

Android/B210 notes

Use a powered USB-C hub/dock. The B210 can brown out or fail to re-enumerate after FX3 firmware jump if powered directly from a phone.

Expected successful flow:

1. Android grants USB permission for the B210/FX3 device.
2. App obtains UsbDeviceConnection fd.
3. UHD loads FX3 firmware if needed.
4. Android re-enumerates the B210 as Ettus Research LLC / USRP B200.
5. App obtains a new fd.
6. UHD opens the B210 and loads FPGA.
7. A FutureSDR flowgraph runs a custom UHD B210 source block into the spectrum sink.
8. UI shows live FFT/waterfall when RX streamer is active.

If the UI says B210 opened; RX stream failed, UHD opened the device but RX streamer setup failed. Replugging or restarting the app is often enough while this Android USB path is still being hardened.

Architecture notes

• Android USB context injection into UHD: docs/android-uhd-injection.md

Fork branches

Patched dependencies are maintained as fork branches:

• https://github.com/m4tsuri/uhd, branch pixdr-android-uhd-4.10
• https://github.com/m4tsuri/uhd-rust, branch pixdr-android
• https://github.com/m4tsuri/Boost-for-Android, branch pixdr-android

Unpatched dependency:

• https://github.com/libusb/libusb, tag v1.0.27

patches/ contains git format-patch exports for review/auditing.