PULP’s CLIC extensions for fast interrupt handling

Overview

Status: Available

• Type: Semester Thesis
• Professor: Prof. Dr. L. Benini
• Supervisors:
  • Robert Balas: balasr@iis.ee.ethz.ch
  • Alessandro Ottaviano: aottaviano@iis.ee.ethz.ch

Introduction

Today’s real-time systems require fast interrupt handling to manage asynchronous requests coming from the surrounding environment. This means that the underlying HW should guarantee a fast propagation of the interrupt line towards the core, with a per-interrupt, fine-grained control over each line, and support interrupt preemption and nesting according to each event priority.

Project

PULPissimo is an open-source, single core RISC-V microcontroller [4] developed by PULP that hosts an industrial-grade processor, namely CV32E40P [3]. RISC-V Core Local Interrupt Controller (CLIC) [2] is a standardized interrupt controller for RISC-V core subsuming the original RISC-V local interrupt scheme (CLINT). It promises pre-emptive, low-latency, vectored, priority/level based interrupts.

The goal of this project is to replace the current interrupt handler in PULPissimo with the CLIC.

In particular:

• Study CLIC reference specifications [2] and PULP’s CLIC implementation [1]
• Integrate PULP’s CLIC into PULPissimo to replace the existing interrupt controller
• Verify basic functional correctness in simulation
• Investigate HW/SW extensions based on known CLIC implementations, such as [5] and [6]
• Synthesize the design, giving particular attention to the CLIC overhead with respect to the original baseline
• ASIC Backend flow towards PULPissimo SoC tapeout

Character

• 15% Literature / architecture review
• 30% RTL implementation
• 30% Backend
• 25% Evaluation

Prerequisites

• Experience with digital design in SystemVerilog as taught in VLSI I
• Must have visited VLSI II in a previous semester or take it alongside the thesis

References

[1] https://github.com/pulp-platform/clic [2] https://github.com/riscv/riscv-fast-interrupt/blob/master/clic.adoc [3] https://github.com/openhwgroup/cv32e40p [4] https://github.com/pulp-platform/pulpissimo [5] https://github.com/bluewww/opene906 [6] https://doc.nucleisys.com/nuclei_spec/isa/eclic.html