BeagleBoard/GSoC/2020 Projects/PRU Improvements

< BeagleBoard‎ | GSoC‎ | 2020 Projects
Revision as of 04:06, 18 April 2020 by Vedant16 (talk | contribs) (changed deliverables)
Jump to: navigation, search

Proposal for Implement a REPL interpreter for PRU

Student: Vedant Paranjape
Mentors: Kumar Abhishek, Jason Kridner
Code: [N/A]
GSoC: [N/A]


This project is currently just a proposal.


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 PRU firmware which only runs some specific user defined commands delivered by RPMSG, executes and then sends a appropriate response. This can be achieved by offloading major task like lexing, parsing to the linux core, and through RPMSG only certain set of commands will be run, the high level code will be converted to these set of commands, on the linux machine itself.


  1. Implement a wrapper library to simplify tasks like writing to a pin, reading from a pin, delay, accessing memory.
  2. Solve issues on am335x_pru_package github.
  3. Update PRUSpeak to work with the latest kernel. Port it to using RPROC and RPMSG, rather than UIO.
  4. Implement a REPL based control for PRU, uses RPMSG and RPROC

Implementation Details

PRU Firmware
PRU will run a firmware which will basically run a while loop, which will evaluate certain specified commands sent to it through RPMSG. Accordingly it will execute the described commands on the PRU. After taking a look at PRUSpeak, its command set enables to do advance PRU control. So, proposed commands set will be
SET_PWM Sets PWM output
SET_OUT Sets HIGH/LOW value of an output pin
READ_IN Reads HIGH/LOW value of an input pin
SET_MEM Sets specified value to specified memory location
READ_MEM Reads value at the specified location
WAIT Waits for given amount of clock cycles
CMP Compares the two operands, returns 0 if equal, -1 if less than and +1 if greater than
ADD Adds two operands.
SUB Subtracts two operands
AND ANDs the two operands
OR ORs the two operands
NOT NOTs the given operand
HALT Stops program execution
Commands will be sent through RPMSG to the PRU and a response, either SUCCESS or error a message, will be sent through RPMSG by the PRU to ARM.

Since PRU is 32 bit, OPCODE will be 8-bit and PARAMS will be 32-bit

Command format
One word commands
Command OPCODE PARAM1 PARAM2 Example Usage
HALT 0x00 N/A N/A HALT Halts the processor
Two word commands
Command OPCODE PARAM1 PARAM2 Example Usage
READ_IN 0x01 Pin Number (Hex format) N/A READ_IN 0x00000007 Reads input at the given input pin.
READ_MEM 0x02 Memory Address N/A READ_MEM 0x80000000 Reads from a given memory location.
WAIT 0x03 Ticks to wait N/A WAIT 0x01113010 Waits for specified ticks
NOT 0x0B register( result stored here) N/A NOT 0x00000007 NOTs the given binary value
Three word commands
Command OPCODE PARAM1 PARAM2 Example Usage
SET_PWM 0x04 PIN Number (Hex format) Duty Cycle (Hex format) SET_PWM 0x00000007 0x0000005A (SET_PWM 7 90) Output PWM pulse on a given pin with specified pulse width.
SET_OUT 0x05 PIN Number (Hex format) HIGH/LOW Value (Hex format) SET_OUT 0x00000007 0x00000001 (SET_OUT 7 1) Sets high/low to the specified pin.
CMP 0x06 Variable A/Constant (Hex format) Variable B/Constant (Hex format) CMP 0x00000008 Ox00000002

Compares A with B gives output:

  • 0x00000000 if A = B
  • 0x00000001 if A > B
  • 0x00000002 if A < B
ADD 0x07 Register (result will be stored here) Register/Constant ADD 0x00000001 0x20202020 Adds two numbers.
SUB 0x08 Register (result will be stored here) Register/Constant SUB 0x00000001 0x20202020 Subtracts two numbers.
AND 0x09 Register (result will be stored here) Register/Constant AND 0x00000001 0x20202020 ANDs two binary values.
OR 0x0A Register (result will be stored here) Register/Constant OR 0x00000001 0x20202020 ORs two binary values.
SET_MEM 0x0C Memory Address Binary data to be written SET_MEM 0x80000000 0x00000011 Writes to a given memory location.


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 PocketBeagle 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