Hyntix USB Flasher

A high-performance, rootless, open-source USB flashing utility for Android. Create bootable Linux and Windows drives directly from your device — no root, no PC required.

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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 clean 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 >4 GB.
• Per-SCSI Progress: physical_position updates after each SCSI WRITE(10) command, polled at 10 Hz 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.
• Linux Persistence (Opt-in): Appends an ext2 casper-rw (Ubuntu, Mint, Pop!_OS) or persistence (Debian Live) partition after the ISO so changes survive reboots. See persistence documentation.
• ISO Validation: File content-probed at selection via Rust probes — only valid Linux or Windows ISOs accepted, with Snackbar feedback for unsupported files.
• USB Verification (Read-Only): Verify any USB drive against its source ISO SHA-256 without re-flashing.
• Backup USB to Image: Create full drive image backup to SAF destination with SHA-256 verification.
• In-App Linux ISO Downloads: Browse 20 distributions, download directly from official mirrors with SHA-256 verification, pause/resume/cancel support.
• Auto-Eject: Drive ejected via SCSI START STOP UNIT on completion.
• Auto Theme: Follows system light/dark theme automatically — no manual toggle needed.
• Ultra-Lightweight: Full APK under 4 MB.

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Architecture

Layer	Description
Android App (:app)	Jetpack Compose UI (MVI-lite). Single MainActivity, single screen with conditional overlays.
Native SDK (:androidusbflasher)	UniFFI + JNA bridge. AndroidUsbFlasher.kt wraps native calls; UsbFlasherNative.kt is auto-generated.
Rust Core (14 crates)	hyntix-usb-flasher-jni (cdylib), hyntix-usb (SCSI BOT, USBDEVFS_BULK), hyntix-usb-flasher (orchestration), hyntix-windows/hyntix-fat32 (UDF/FAT32), hyntix-iso/udf/wim (parsers), hyntix-storage/partition/persistence (block devices, partition editing, ext2 persistence).

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Performance

Metric	Value
USB 2.0 ceiling	~19 MB/s write, ~20 MB/s read verify (NAND-limited on typical flash drives)
Initial burst	Pipeline starts at 4 MB chunks, AIMD settles at stable size (4–16 MB on typical devices)
DMA constraint	Most Android devices have usbfs_memory_mb < 8 MB, forcing small URB sizes in legacy SUBMITURB/REAPURB pipelines. USBDEVFS_BULK bypasses this by delegating DMA to the kernel.
Initial chunk	4 MB (configurable via INITIAL_URB_CHUNK_SIZE)
Max SCSI transfer	16 MB (SCSI_MAX_TRANSFER_SIZE)
Buffer pool	4 × 32 MB = 128 MB total

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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 0.32.2 --features cli

3. Build:

   ./gradlew assembleRelease

4. APK at app/build/outputs/apk/release/app-arm64-v8a-release.apk

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Usage

1. Select ISO: Tap the image card → choose Download ISO (Linux) or Choose from device (Windows/Linux local files).
2. Download (Linux): Pick distribution/variant → choose SAF destination → download starts with SHA-256 verification.
3. Select USB: Connect USB drive via OTG → grant permission → drive appears in target card.
4. Optional — Persistence (Linux live ISOs only): Enable persistence toggle, choose size, confirm.
5. Flash: Tap Erase and Flash → confirm → progress sheet shows real-time speed, ETA, progress.
6. Verify (optional): After flash or anytime, use Verify USB to SHA-256 compare the drive against the source ISO.
7. Backup (optional): Use Backup USB to create a full drive image (.img) with SHA-256.

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Supported Distributions (In-App Catalog)

Family	Distributions
Debian-based	Debian, MX Linux, Kali Linux, antiX, Deepin, Parrot OS
Ubuntu-based	Ubuntu, Linux Mint, Pop!_OS, Zorin OS, Linux Lite
Arch-based	Arch Linux, Manjaro, Garuda Linux, CachyOS
Fedora-based	Fedora, Nobara, Qubes OS
Other	openSUSE Tumbleweed, NixOS

20 distributions, 52 variants total. Persistence supported for casper (Ubuntu/Mint/Pop!_OS) and Debian Live images.

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Limitations

• ARM64 Android devices only (API 33+ / Android 13+)
• Windows ISOs: flash from local storage only (in-app download not supported)
• Linux persistence: unencrypted; casper (Ubuntu/Mint/Pop!_OS) & Debian Live only; no Fedora, Arch, openSUSE, Kali, Tails, Parrot, Ventoy, 4Kn drives
• No root, no PC required

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Building from Source

Prerequisites

• Android NDK r28+
• Rust 1.85+ (rustup target add aarch64-linux-android)
• uniffi-bindgen 0.32.2: cargo install uniffi --version 0.32.2 --features cli
• Android Studio / Gradle 9.x

./gradlew assembleRelease
# APK at: app/build/outputs/apk/release/app-arm64-v8a-release.apk

Rust-only build

cd androidusbflasher/rust-lib
cargo build --release --target aarch64-linux-android -p hyntix-usb-flasher-jni

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License

GPL-3.0. See LICENSE.

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Contributing

See CONTRIBUTING.md and CODE_OF_CONDUCT.md.

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Security

See SECURITY.md for vulnerability reporting.

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Built with ❤️ by the Hyntix team.