BeagleBoard/GSoC/2020 Projects/PRU Improvements

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Proposal for Implement a REPL interpreter for PRU

Student: Vedant Paranjape
Mentors: Kumar Abhishek, Pratim Ugale, Andrew Henderson
Code: [N/A]
GSoC: [N/A]


This project is selected for GSoC 2020


Completed all the requirements listed on the ideas page. the code for the cross-compilation task can be found here submitted through the pull request #138.

About you

IRC: vedant16
School: Veermata Jijabai Technological Institute (VJTI)
Country: India
Primary language : English, Hindi, Marathi
Typical work hours : 10AM - 7PM Indian Standard Time
Previous GSoC participation: I find embedded pretty interesting, given I have experience with ESP32, I think I will be able to excel in this project. This is the first time i am participating in GSoC

About your project

Project name: Implement a REPL interpreter for PRU


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 Bhilack, the PRU is ideal for offloading IO intensive tasks.
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 it keeps many creative developers away. So, I propose to implement a REPL based control of the PRU, hiding all the low level things behind the REPL and providing a clean interface to uses PRU.
This can be achieved by implementing a language on top of the PRU Assembly. It will directly compile down to PRU assembly. This could also be solved by implementing a bytecode engine on the PRU, but this will result in waste of already limited resources on PRU. With this approach, both PRU cores can be run independent of each other.


  1. Implement a language for PRU which compiles down to PRU Assembly.
  2. Solve issues on am335x_pru_package github.
  3. Update PRUSpeak to work with the latest kernel.

Implementation Details

Implement a language for PRU which compiles down to PRU Assembly.
  • Language Name: SimpPRU
  • Statically typed language
  • TAB or 4 spaces for indentation
Primitive data types
  • `int`
  • `bool`
Binary operators
  • `/` divide
  • `*` multiply
  • `+` plus
  • `-` minus
Unary operators
  • `&` unary and
  • `|` unary or
  • `~` unary not
logical operator
  • `and` logical and
  • `or` logical or
  • `not` logical not

operator precedence, as arranged

Arithmetic operations
  • `int` and `float` can be operated together, `int` will be promoted to float
  • `bool` cannot be operated with anything other than `bool`
  • `bool` only supports unary operators
Variable assignment
  • `<data_type> <identifier> := <value>`
  • int value := 34
if elif else loop
   if <condition_to_be_evaluated>:
       <do something>
   elif <condition_to_be_evaluated>:
       <do something>
       <do something>
for loop
   for <identifier>, <condition>, <action to loop completion>:
       <do something>
   <return type> <function name> ( variable name, ...):
       <do something>
   int add(int a, int b):
       return a + b
  • Each functions must always return something, since void data type is not included
Register Access
   bool read_register(register_name, bit_to_be_read)
   bool write_register(register_name, bit_to_be_written, bool value_to_be_written)
Solve issues on am335x_pru_package github
  1. Solve issue #44, #41, #49


May 4 Proposal accepted or rejected
  • Community Bonding Period and discussion on the project and resources available.
  • Complete this course, which teaches how to build a assembler, lexer, parser.
  • Go through the given tutorials to learn about building a programming language:
  1. A Python interpreter written in Python
  2. Simple iterator based parser
  3. Simple top down parsing in python
  4. Lets build a simple interpreter
  5. Make Your Own Simple Interpreted Programming Language
  6. Write a C interpreter
June 1 Pre-work complete Coding officially begins!
June 8 Milestone #1
  • Introductory YouTube video
  • Setting up BeagleBone Black Wireless i.e flashing up to date Linux image and Testing user-led blink code :D
  • Running existing example codes from this repository
June 15 Milestone #2
  • Implementing HALT and WAIT functions.
  • Testing the above functions
  • Writing documentation for same
  • Setting up documentation generators like readthedocs
June 22 Milestone #3
  • Implementing SET_PWM, SET_OUT, READ_IN functions.
  • Testing the above functions
  • Writing documentation for same
June 29 - July 3 18:00 UTC Milestone #4 (Phase 1 evaluations)
  • Finalizing and documenting everything done till now, submitting first report for evaluation
July 10 Milestone #5
  • Implementing READ_MEM, SET_MEM functions
  • Testing the above functions
  • Writing documentation
July 17 Milestone #6
  • Implementing ADD, SUB functions
  • Testing the above functions
  • Writing documentation
July 24 Milestone #7
  • Implementing CMP, AND, OR functions
  • Testing the above functions
  • Writing documentation
July 27 - July 31 18:00 UTC Milestone #8 (Phase 2 evaluations)
  • Finalizing and documenting everything done till now, submitting second report for evaluation
August 3 Milestone #9
  • Implementing NOT function
  • Testing the above functions
  • Writing documentation
August 10 Milestone #10
  • Completing the documentation
  • Taking feedback from mentors
August 17 Milestone #11 Completion YouTube video
August 24 - August 31 18:00 UTC Final week Students submit their final work product and their final mentor evaluation
August 31 - September 7 18:00 UTC End of Session Mentors submit final student evaluations

Experience and approach

I have decent experience in C++, C and Python. I have done several projects involving embedded systems like ESP32, I well-versed with freeRTOS. I recently did a project on ESP32, in which I used ESP to control and plot PID loop running on the embedded device, plotting the values on a python GUI. Other than that I have developed firmware for a 3 DOF arm based on a ESP32 custom board. I did a internship with a embedded deviced startup, where I built:

  1. Built TCP network stack for embedded IoT Devices
  2. Implemented Synchronous TCP server using Boost.Asio(C++) and Boost.Thread(C++)
  3. Implemented a tool to calculate round trip time(RTT) of tcp packets

I actively contribute to open source and do a lot of mini projects throughout the year, you can find my several more interesting projects at my github page


I believe that if I get stuck on my project and my mentor isn’t around, I will use the resources that are available to me. Some of those information portals are listed below.

  2. PRU Guide
  3. Mark Yoder's cookbook is a excellent guide
  4. Derek Molly's beagle bone guide provides all the information needed for getting up and running with my beagle.
  5. The technical reference manuals provided by TI on am3358 and am5729 are the best source
  6. Processor SDK Linux Software Guide is a good reference material


Currently interfacing with the PRU requires a lot of makefile manipulation, kernel drivers and stuff. There's no working around that for more advanced applications but if you can get something simple up and running quickly with a REPL, that'd be great.
-Abhishek Kumar