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PoliLEG

Simplified, monocycle version of the LEGv8 processor designed by the Department of Computer and Digital Systems Engineering (PCS) at Escola Politécnica da Universidade de São Paulo (Poli-USP) and implemented in VHDL for Digital Systems II (PCS3225) in 2021.

Waveform resulting from Fibonacci and GCD execution in PoliLEG

Requirements

  • GHDL
  • hdlmake
  • GTKWave (optional, used for visualising generated waveforms as shown above)

Build

The build process once hdlmake is installed is straightforward:

  1. Clone this repository
git clone https://github.com/tomaz-suller/PoliLEG.git
  1. Enter the simulation directory and build with hdlmake
cd simulation
hdlmake makefile
make

The default options will run fibonacci and automatically open GTKWave to show the generated waveform using the configuration file supplied (fibonacci.gtkw). This behaviour can be altered by editing simulation/Manifest.py and by then recreating the Makefile as described previously.

Usage

Running other software

PoliLEG can only execute a small subset of the ARMv8 instructions. Namely, it can only execute the following functions, with their respective formats and opcodes for reference. More detailed information can be found in the Green Card of LEGv8.

Instruction Format opcode
LDUR D 11111000010
STUR D 11111000000
CBZ CB 10110100
B B 000101
ADD R 10001011000
SUB R 11001011000
AND R 10001010000
ORR R 10101010000

Therefore, any software must be specifically designed to only use these instructions. As this processor was developed for educational purposes, the supplied software (fibonacci and gcd) were handwritten in LEGv8 Assembly and then manually converted to machine code.

Copying standalone components

Any component is avaliable for use in other projects if and only if these projects comply with this software's LICENSE. Most importantly, it is work noting that your work must disclose its full source if it uses any part whatsoever of this software.

It is also worth noting this repository is NOT meant to provide ready-made implementations for the course's projects. Therefore, this software cannot be submitted as proof of your own work, and any known attempts to do so will be reported immediately without exception.

Repository Structure

Directories were set up according to hdlmake's example setup.

  • github: media content used in the README;
  • modules: hardware descriptions of components used to build the processor, including a dummy toplevel implementation for testing purposes;
  • simulation: files related to simulation with GHDL ( hdlmake's Manifest.py and GTKWave configuration files);
  • software: content of both the instruction memory (rom.dat) and the data memory (ram.dat). A GCD calculator using Euclides' Algorithm (gcd) and a Fibonacci sequence generator (fibonacci) are supplied;
  • testbenches: testbenches for hardware descriptions following the directory structure of modules. Note that all components have testbenches with assertions (i.e. automatically produce a pass or fail message on execution) except for polilegsc, datapath and toplevel.

References

D. Patterson and J. Hennessy. Computer Organization and Design ARM Edition: The Hardware Software Interface. The Morgan Kaufmann Series in Computer Architecture and Design. Elsevier Science, 2016.