bsod2528 / cpu

a simple risc processor

cpu

Documentation | Blogs

VR16, a basic RISC processor designed and written in verilog. As time permits, this will be made better and backend design will also be updated.

Features

• single stage cpu
• each instruction is 16-bit.
• 4 general purpose registers (r0, r1, r2, r3).
• runs on custom instruction set architecture called vr-isa.
• vr-asm as assembly and vrscript for writing easier code to run on the cpu.

Warning

The isa is very much work in progress, so things are subject to change. Documentation for vr-asm and vrscript may or may not be up-to-date due to extensive prematurity of their presence.

Setup

On how to run this project in your local machine.

Windows

1. Install WSL and install gtkwave and iverilog.
2. Setup venv in root directory.
3. Run ./compile.sh and then ./sim.sh to view the rtl waveforms.

Linux

1. Install gtkwave and iverilog.
2. Setup venv in root directory.
3. Run ./compile.sh and then ./sim.sh to view the rtl waveforms.

Road-Map

• finish basic cpu
• pipeline it
• finish physical design

As of 13-10-2025 basic cpu is 90% done, just a bit more debugging is needed.

Basic docs for VRASM and VRSCRIPT

VRASM

1. Actual programs start generating machine code by starting the code with start:, similary to stop generating machine code use end:.
2. Comments can be made using --.
3. For program syntax, kindly refer isa.md

VRSCRIPT

1. Variables: `<var_name> =
2. All instructions are accessed by calling respective functions: `(, [arg])
3. Iterative loops will be coming soon.

Licensing

There are three parts to this CPU:

• frontend
• backend
• toolchain

1. Frontend deals with the synthesizable code written in verilog, the rtl and the corresponding testbenches, which are licensed under GPLv3.
2. Backend (will start soon) deals with the actual physical design of the cpu, which will be licensed under the CERN-OHL-S.
3. Toolchain deals with the software side of the project, the assembler/ and compiler/ which makes programming on the CPU, which also come under GPLv3.