Snapmaker U1 Custom Kernel Builder

Custom kernel builds for Snapmaker U1 3D Printer

Overview

This project builds custom Linux kernels compatible with the Snapmaker U1 3D printer. Kernel is built from Rockchip's official sources with Snapmaker-specific device tree and configurations.

All actions are performed through the dev.sh script. Try not to run any other scripts or commands directly because it shouldn't be necessary for normal workflows.

Prerequisites

• Docker or Podman
• ~5GiB free disk space
• Linux host (it's containerized, but we haven't tested macOS or WSL)
• (Optional) QEMU with KVM support for testing kernels in virtual machines

First time setup

Also use these commands with more arguments to update tools or kernel source later. Use ./dev.sh help and ./dev.sh <command> help for more information.

./dev.sh prepare tools
./dev.sh prepare kernel
./dev.sh prepare proprietary
./dev.sh prepare rootfs       # Optional, only needed for running the kernel in virutal machines

Build The Kernel

# Build production kernel
./dev.sh make kernel
# OR:
./dev.sh make kernel PROFILE=open

# Build a specific version of development kernel (for virtualization testing)
./dev.sh make kernel PROFILE=open-devel KVER=6.1

Existing Build Profiles

open

Intended for production use on Snapmaker U1 printer instead of stock kernel.

• Uses Snapmaker's stock kernel configuration as base
• Enables Rockchip-specific drivers for display and security features
• Adds support for being containerization and virtualization host
• Adds support for running as virtualized guest
• Adds networking and storage drivers

open-devel

Intended for development, debugging, and testing on hardware and in virtual machine.

• All features from open profile
• Adds Kernel Debugging and development tools
• Disables DRM and security features necessary to run in virtual machine

Don't use open-devel profile in production because it disables important drivers. Always use open-devel profile when testing in virtualization environments.

Kernel Versions

Currently only 6.1. series works. In the future we'll be trying to go for 6.6 and possibly mainline but that's a long shot because of missing Rockchip drivers.

Build System

Make Targets

./dev.sh make help                              # Show all targets
./dev.sh make kernel PROFILE=open KVER=6.1      # Production build
./dev.sh make kernel PROFILE=open-devel KVER=6.1 # Development build
./dev.sh make clean                             # Remove build artifacts

Testing In Virtualization

Currently only supports QEMU and requires Linux host with KVM and virtio support. Instructions for testing on Mac or Windows are very much welcome; please contribute!

./dev.sh prepare rootfs download    # Download latest rootfs tarball
./dev.sh prepare rootfs image       # Create disk image from downloaded tarball
./dev.sh prepare rootfs modules     # Update kernel modules in existing rootfs
./dev.sh prepare rootfs v1.0.0      # Download specific version and create image

# Note: Use -devel profile for virtualization compatibility

# Auto-detect newest -devel kernel with default profile
./dev.sh run

# Auto-detect with specific profile
./dev.sh run qemu-gui

# Explicit kernel with default profile
./dev.sh run output/kernel-open-devel-6.1-20260111-abc1234-vmlinuz

# GUI profile (with virtio-gpu graphics)
./dev.sh run qemu-gui output/kernel-open-devel-*-vmlinuz

Press Ctrl-A X to exit QEMU (console profile) or Ctrl-Alt-G to release mouse grab (GUI profile).

Build Scripts

These scripts are not intended to be run directly. Use ./dev.sh as the main entry point.

scripts/clone-rockchip-kernel.sh

Clones the Rockchip kernel source. Run this once before building and whenever you want to update the source.

./dev.sh prepare kernel 6.1

scripts/build-kernel.sh

Main kernel build. Build and starts container to ensure consistent build environment.

./dev.sh make kernel PROFILE=open KVER=6.1

Process:

1. Patches kernel version
2. Copies device tree
3. Configures kernel with snapmaker-u1-stock.config
4. Applies profile-specific config fragments
5. Builds kernel, DTB, and modules
6. Patches proprietary modules
7. Creates FIT boot image

scripts/kernel-config.sh

Centralized configuration (sourced by other scripts).

Defines:

• KERNEL_PROFILES - Associative array of config fragments
• get_kernel_branch() - Maps version to git branch
• validate_profile() - Validates profile names

scripts/run-virt.sh

Runs built kernels in virtual machines for testing. Optionally uses rootfs image to also test from userspace.

MUST use -devel kernel profile because standard profiles include Rockchip-specific features which can't be virtualized.

Virtualization Profiles

Two QEMU on Linux profiles are available (selected via profile argument to run command):

qemu-console (default)

No graphics, serial console only. Use when quickly testing if the new kernel boots.

qemu-gui

GUI profile with graphics

Usage

# First build -devel kernel
./dev.sh make kernel PROFILE=open-devel

# Get and prepare rootfs for VM testing
./dev.sh prepare rootfs download
./dev.sh prepare rootfs image
./dev.sh prepare rootfs modules

At this point rootfs has been downloaded, converted to disk image, init patched to preload kernel modules from modules.img disk.

# Run qemu virtual machine with newest *-devel kernel from output/ directory
./dev.sh run

# Run with graphics enabled
./dev.sh run qemu-gui

# Run an alternative kernel
./dev.sh run output/kernel-open-devel-*-vmlinuz

Interactive Console Controls for QEMU

• Console-only profile
  • Ctrl-A X - Exit QEMU
  • Ctrl-A C - Switch to QEMU monitor console
• GUI profile
  • Ctrl-Alt-G - Release mouse/keyboard grab
  • Ctrl-Alt-1 - Switch to virtual console
  • Ctrl-Alt-2 - Switch to QEMU monitor

Development

Modifying Kernel Configurations

Create or edit profiles in config/profile-*.config: Then add the profile to scripts/kernel-config.sh:

KERNEL_PROFILES=(open open-devel my-custom)

Modifying Device Tree

Edit config/snapmaker-u1-stock.dts. Changes will be copied to the kernel tree during build.

Debugging Builds

Use the open-devel profile for debug symbols, additional diagnostics, and virtualization compatibility:

./dev.sh make kernel PROFILE=open-devel KVER=6.1

Build artifacts remain in tmp/kernel-* on failure for inspection.

Troubleshooting

Kernel source not found

Error: Kernel source not found at rockchip-kernel

Solution: Clone the kernel source first

./dev.sh prepare kernel 6.1

Build failures

Check tmp/kernel-$$ for build logs. The build directory persists on error.

Kernel doesn't boot in virtualization

Ensure you're using the open-devel profile (requires VirtIO drivers and has Rockchip DRM/security disabled):

./dev.sh make kernel PROFILE=open-devel KVER=6.1
./dev.sh run output/kernel-open-devel-6.1-*-vmlinuz