In addition, other instructions can be extended to suit the application. The basic integer operations should be implemented in all platforms. I implemented RV32I instructions, which defines basic integer operations for 32-bit architecture. In hardware, arithmetic operations such as addition and subtraction are performed by ALU (Arithmetic logic unit), but in the emulator I decided to implement it without worrying about small components. Execute: Performs the action required by the instruction.How to interpret the instruction is defined in Volume I: Unprivileged ISA at /specifications. Decode: Splits an instruction sequence into a form that makes sense to the CPU.Fetch: Fetches the next instruction to be executed from the memory where the program is stored.The role of a CPU is to execute a program consisting of binaries sequentially by three steps: fetching, decoding, and execution. First, I’m going to implement a CPU instruction one by one by reading Volume I: Unprivileged ISA in the specifications. RISC-V is an open standard instruction set architecture, and you can download PDFs of the specification from /specifications. I implemented add instruction to add two registers, and addi instruction to add registers and a 12-bit immediate value. There’s nothing yet to function as an emulator. Wasm-bindgen imported in src/lib.rs is the library to communicate with Rust and JavaScript. I used the template in the tutorial of Rust and WebAssembly because I wanted to use Rust for my curiosity and compile it to WebAssembly to run the emulator in the browser. This is the first commit after creating a repository. Note: The source code at each point in time is not necessarily the correct implementation, as I sometimes fixed implementation errors after the commit. In this article, I’m going to introduce emulator’s features implemented for running the OS, by looking back at the source code that made major changes. All the source code of the emulator is available in the d0iasm/rvemu repository. I’ve made a RISC-V emulator that can run xv6, a simple Unix-like OS for education.

Riscv qemu tutorial