Hyntix USB Flasher

A high-performance, rootless, open-source USB flashing utility for Android. Enables creating bootable Linux and Windows drives directly from your device.

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Key Features

• Direct SCSI Engine: Rust core using USBDEVFS_BULK synchronous ioctl — kernel manages DMA internally, bypassing the usbfs_memory_mb userspace pool limit.
• Adaptive AIMD Flow Control: Chunk size halves on ENOMEM, additively recovers after 200 cycles, but never exceeds last_failing_size / 2. Prevents 64KB-128KB DMA oscillation.
• Windows Deployment Core: Full Windows 10/11 ISO support with FAT32 formatting and intelligent WIM/SWM splitting for files >4GB.
• Per-SCSI Progress: physical_position updates after each SCSI command, polled at 10Hz from the main thread — smooth UI without jank.
• BLAKE3 Verification: Triple-buffered read-ahead verification with BLAKE3 hashing computes integrity check inline during source reads.
• ISO Validation: File content-probed at selection via Rust probes — only valid Linux or Windows ISOs accepted, with Snackbar feedback for unsupported files.
• Ultra-Lightweight: Full APK under 3MB.
• Auto-Eject: Drive ejected via SCSI START STOP UNIT on completion.

Architecture

1. Android App (:app): Jetpack Compose UI (MVI-lite). Single MainActivity, single screen with conditional overlays.
2. Native SDK (:androidusbflasher): UniFFI + JNA bridge. AndroidUsbFlasher.kt wraps the native calls; UsbFlasherNative.kt is auto-generated.
3. Rust Core (11 crates):
   • hyntix-usb-flasher-jni: CDYLIB entry point, UniFFI exports -> libusbflasher.so
   • hyntix-usb: SCSI BOT protocol, USBDEVFS_BULK with AIMD flow control
   • hyntix-usb-flasher: Flash orchestration, BLAKE3 verification, progress polling
   • hyntix-windows, hyntix-fat32: UDF parsing, FAT32/GPT formatting, WIM splitting
   • hyntix-iso, hyntix-udf, hyntix-wim: Filesystem parsers

Performance

• USB 2.0 ceiling: ~19 MB/s write, ~20 MB/s read verify (NAND-limited on typical flash drives)
• Initial burst: Pipeline starts at 256KB chunks, AIMD settles at stable size (64KB on constrained DMA pools, 128KB+ on larger pools)
• DMA constraint: Most Android devices have usbfs_memory_mb < 8MB, forcing small URB sizes in a SUBMITURB/REAPURB pipeline. USBDEVFS_BULK bypasses this by delegating DMA to the kernel.

Getting Started

Prerequisites

• Android 13+ (API 33)
• USB-OTG adapter + flash drive

Building from Source

1. Install Android NDK r28+, Rust 1.85+, rustup target add aarch64-linux-android
2. Install uniffi-bindgen matching the crate version: cargo install uniffi --version 0.31.2 --features cli
3. Build: ./gradlew assembleRelease
4. APK at app/build/outputs/apk/release/app-arm64-v8a-release.apk

License

GPL-3.0. See LICENSE.