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Vedant Paranjape edited this page Aug 25, 2020 · 33 revisions

simpPRU

This is Google Summer of Code 2020 project under beagleboard.org aimed at achieving:

  1. Provide a simple to use language to write code for the PRU
  2. Provide a simple to use way to start/stop PRU and send/receive messages through RPMSG framework, without the need to write to various sysfs interfaces

Project Details

Table of contents

Brief overview of PRU-ICSS

The PRU is a dual core micro-controller system present on the AM335x SoC which powers the BeagleBone. It is meant to be used for high speed jitter free IO control. Being independent from the linux scheduler and having direct access to the IO pins of the BeagleBone Black, the PRU is ideal for offloading IO intensive tasks.

It is a low-latency microcontroller subsystem, which provides real-time processing capability lacking in Linux. PRUs are part of the PRU-ICSS, “Industrial Communications SubSystem”. They are free from running on an operating system, and thus can be dedicated to a single function.

The PRU cores were created to be non-pipelined, single-cycle execution engines. This means that all instructions (except for memory reads and writes) complete in a single cycle. Since there is no pipeline, the PRU cores are completely deterministic: the PRU cores will not rearrange instructions during execution.

The PRU-ICSS can also read from or write to external pins in a single cycle using a PRU core register (R30/R31). With a PRU core running at 200 MHz, this means that an external signal change can be detected in as little as 5 nanoseconds. This also means that the PRU can toggle external pins with as fast as 5 nanoseconds.

The PRU-ICSS also has an interrupt controller, it does not support asynchronous interrupts as they introduce jitter in execution time and reduce determinism. Instead it supports an efficient polling system.

What was the need for simpPRU ?

Programming the PRU is a uphill task for a beginner, since it involves several steps, writing the firmware for the PRU, writing a loader program. This can be a easy task for a experienced developer, but intimidating for a beginner.

This problem was solved earlier by pruspeaks project, but it inflicts serious restrictions on PRU, as PRU0 runs a bot speaks interpreter and PRU1 takes care of generating PWM signals. Already PRU has meagre resources, so emulating a VM on top of PRU leaves very less room to use PRU for what it is meant, deterministic control and fast read writes.

How does simpPRU simplify things ?

Implementation details of simpPRU

Building from source

Dependencies

  • flex
  • bison
  • gcc
  • gcc-pru
  • cmake

Build

git clone https://github.com/VedantParanjape/simpPRU.git
cd simpPRU
mkdir build
cd build
cmake ..
make

Install

sudo make install

Build debian package

sudo make package

Installation from debian package

Download

Download the latest debian package from: https://github.com/VedantParanjape/simpPRU/releases/latest Download amd64 package for x86_64 systems and armhf package for arm32v7 systems

Install

sudo dpkg -i simppru-<version_number>-amd64.deb

  • replace <version_number> with the appropriate version of the downloaded package

Work Summary

Things to be implemented in Future

Conclusion

Known Issues

Notes

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