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RTMux is a lightweight open source para-virtualization layer, using resource-multiplexing techniques to provide a highly deterministic real-time environment for Linux/ARM. Typically, less than 500 lines modication against Linux kernel are required to allow additional RTOS executives on the same ARM core concurrently with real-time performance guarantees.

• Build RTMux-friendly RTOS
  • RT-Thread Lite is the only RTOS supporting RTMux.
  • SCons is required to build RT-Thread Lite.
  • Fetch the source
    • git clone https://github.com/rtmux/rt-thread-lite.git rt-thread && cd rt-thread
  • Configure and Build for the machines. Take Realview for ARM Cortex-A8 for example:
    • cd bsp/realview-a8 && scons
  • Copy the generated file rtthread.bin to the path /tmp/rtos.bin
• Modifying Linux kernel is vital, and get the kernel source in advance. The version that RTMux supports is v3.8.13
  • Apply the patches under directory patches/ against Linux source
  • patch -p1 < patches/0001-RTMux-implement-dual-kernel-approach-in-minimal-chan.patch
  • patch -p1 < patches/0002-RTMux-support-Realview-Platform-Baseboard-for-Cortex.patch
  • patch -p1 < patches/0003-RTMux-support-AM33x-based-platforms.patch
  • patch -p1 < patches/0004-arm-gic-correct-the-cpu-map-on-gic_raise_softirq-for.patch
• Enable ARM_VMM in kernel configurations.
  • make menuconfig ARCH=arm
  • At present, both Realview for ARM Cortex-A8 and Beaglebone Black (based on TI AM33x) are supported.
• Build the kernel image
  • make ARCH=arm CROSS_COMPILE=arm-none-eabi- zImage
• Build the virtual machime monitor module for Linux
  • make -C <kernel-source-path> M=$PWD ARCH=arm CROSS_COMPILE=arm-none-eabi-
• Repack the root filesystem and ensure the following changes:
  • Copy the generated rtvmm.ko
  • Put the RTMux-friendly RTOS image (that is, /tmp/rtos.bin) under the path /vmm/rtos.bin.

• Insert vmm kernel module when you are about to launch the RTOS
  • insmod rtvmm.ko
• Linux domain would continue executing, and the real-time domain starts as expected.