Arch R - Project Documentation

Project Overview

Arch R is a custom Arch Linux ARM-based gaming distribution for the R36S handheld console.

Hardware Support

SoC: Rockchip RK3326
Display: 640x480 (rotated portrait)
USB OTG: Host mode with VBUS power control
Wi-Fi: AIC8800 USB adapter (with modeswitch support from a69c:5721 to a69c:8801)
Multiple R36S hardware revisions: Multiple DTB support planned

Build Requirements

Ubuntu 22.04+ or Arch Linux
Cross-compilation toolchain (aarch64-linux-gnu-gcc)
Device Tree Compiler (dtc)
QEMU for ARM64 userspace emulation
~10GB disk space

Build Process

Setup toolchain: sudo ./setup-toolchain.sh
Source environment: source env.sh
Build kernel: ./build-kernel.sh
Build rootfs: sudo ./build-rootfs.sh
Build image: sudo ./build-image.sh

Key Technical Notes

USB OTG Configuration

The R36S (when using RG351MP-based firmware) had USB OTG issues due to:

otg-port status set to "disabled" in Device Tree
dr_mode set to "otg" instead of "host"
Missing vbus-supply reference to otg_switch regulator (phandle 0xec)

Solution: Modify Device Tree to:

usb@ff300000 {
    dr_mode = "host";  // Force host mode
};

otg-port {
    status = "okay";    // Enable OTG port
    vbus-supply = <&otg_switch>;  // Reference power regulator
};

Wi-Fi Modeswitch

The AIC8800 USB adapter appears first as a CD-ROM device (VID:PID a69c:5721). A udev rule triggers /usr/bin/eject to switch it to Wi-Fi mode (a69c:8801).

See: config/udev/99-archr-r36s.rules

Multiple R36S Revisions

The R36S has multiple hardware revisions requiring different Device Trees. The build system should be updated to:

Include all DTB variants in /kernel/dts/
Auto-detect hardware revision at boot
Load appropriate DTB

Directory Structure

arch-r/
├── bootloader/          # U-Boot configuration
│   └── configs/
├── kernel/              # Kernel and Device Trees
│   ├── configs/         # Kernel defconfig
│   ├── dts/             # Device Tree sources/binaries
│   └── patches/         # Kernel patches
├── rootfs/              # Root filesystem
│   └── overlay/         # Files to overlay on rootfs
├── config/              # System configuration
│   ├── retroarch.cfg    # RetroArch config for R36S
│   └── udev/            # udev rules
├── scripts/             # Runtime scripts
└── output/              # Build artifacts

References

Kernel: dArkOS kernel source (4.4.189)
Base system: Arch Linux ARM aarch64
Frontend: RetroArch + EmulationStation

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