rkarsnk / multiplix

An operating system kernel for RISC-V and AArch64 SBCs

Multiplix kernel

Multiplix is a small operating system serving as the foundation for some research projects in operating systems. It is currently designed as a monolithic kernel plus a special kernel monitor that runs at a higher privilege level. Multiplix is very much in-progress.

At the moment it is too early to have in-depth instructions on how to set up Multiplix. After more continued development this page will be expanded, so stay tuned! (estimate: check back in 1-3 months for more information)

The current status is that Multiplix can boot all cores, enable virtual memory and interrupts, and supports multiple user-mode processes with a limited set of system calls. On the Raspberry Pis Multiplix also has an SD card driver and a read-only FAT32 file system. Current work is focused on expanding the system call interface to support a shell and a basic user-mode environment.

Supported systems

Multiplix supports RISC-V and Armv8, specifically on the following hardware:

• VisionFive: 2-core SiFive U74 1.0 GHz.
• VisionFive 2: 4-core SiFive U74 1.5 GHz (plus a 5th SiFive S7 monitor core).
• Raspberry Pi 3: 4-core ARM Cortex A53 1.4 GHz.
• Raspberry Pi 4: 4-core ARM Cortex A72 1.5-1.8 GHz.

Support for more boards is likely to be added in the future (Ox64, and more of the Raspberry Pi family).

Building

To build multiplix you must have a GNU bare-metal toolchain and either LDC or GDC. You can get everything you need (prebuilt) from multiplix-toolchain-linux-amd64.tar.gz. You must also have Go installed to build the plboot tool (for creating bootloader payloads).

Multiplix uses the Knit build tool. The Knitfile has the following targets:

• kernel.bin: build the kernel binary.
• kernel.boot.bin: build the bootable kernel binary (kernel binary embedded in the bootloader as a payload).
• qemu: emulate the kernel using QEMU (requires qemu-system-riscv64 or qemu-system-aarch64).
• bootloader.bin: build the kernel bootloader.
• prog: send the kernel over UART to the bootloader.

You can configure the build for a specific board by specifying setting the board variable to raspi3, raspi4, visionfive, visionfive2, or virt_riscv64 (e.g., knit board=raspi3).

Specify the D compiler with dc. Supports dc=ldc2 or dc=gdc.

For example: knit qemu board=virt_riscv64 dc=ldc2 will build a kernel targeting the QEMU virt machine with LDC and run it in QEMU.

The lto option configures whether the kernel is built with link-time optimization (requires the LLVMgold linker plugin for use with LDC).

The unified option controls whether the build is done as a single compilation unit (one invocation of the D compiler), or in parallel with multiple compilation units.