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GSoC 2020 Blog

GSoC 2020 Final Report

This report summarises the work that I have done during Google Summer of Code 2020.

Project Overview

The objective of the project is to improve the Beaglebone Board Support Package (BSP) in RTEMS by adding a Flattened Device Tree (FDT) based driver initialization and refactoring the present drivers to use FDT based initialization. This will make the BSP more generic, and hence adding support for future board variants becomes easier. The other major goal of the project is to port the FreeBSD pinmuxing driver to RTEMS.

The goal of the project is to fix the following tickets

  1. #3784
  2. #3782

RTEMS wiki: wiki

Mentors:

  1. Christian Mauderer
  2. Vijay Kumar Banerjee
  3. Amaan Cheval

Project Objectives

  1. Add/Port Beagle pinmux driver to RTEMS.
  2. Refactor the BSP drivers to use FDT based initialization.
  3. Unify the BSP

Summary

By the end, I finished importing the Beagle clock and pinmux driver into RTEMS, implemented the RTEMS OFW API(FDT only implementation) and FreeBSD structures to make the porting of driver easy and finally refactored the Beagle i2c driver. I will refactor rest of the driver post GSoC.

Below I have summarized the work done in each phase and also the changes and challenges that were encountered.

The project didn’t go as it was proposed, there were a lot of unexpected changes.

Phase One

As per the proposal, the goal of the first phase was to port, test the pinmux driver with libBSD and to implement a few OFW functions which were majorly used. But after a few discussions with other community members, porting the OFW API to RTEMS instead of just implementing a few functions seemed like a good idea. This resulted in me porting the OFW API to RTEMS. Once this was done I ported the pinmux driver to RTEMS.

And while porting the pinmux driver, I compared it to other ported drivers, there were lot of similarities so we also decided to implement a few structures and functions which will help to reduce the amount of work done in porting a driver. I have also written a blog post about it here.

During this time RTEMS was planning to move to a WAF based build system. So as per suggestions of my mentor I rebased all these patches to the new build system and had also written a blog about it.

I am not posting any links to my commits because there underwent a lot of changes in the later weeks hence I have decided to post them in last.

Outcomes of phase 1:

  1. Ported the OFW API to RTEMS
  2. Ported the Beagle pinmux driver to RTEMS
  3. Implemented FreeBSD structures to make porting easy.

Phase Two

In this phase, I started testing the pinmux driver, this work actually started in phase one but libBSD refused to build with the new build system, so I had wait until it got resolved. Finally during the second week of the phase 2 the issue got resolved and I was able to test the pinmux driver. Also the first few weeks were spent in fixing bugs and improving the FreeBSD structures implemented in RTEMS. And the last couple of weeks was spent in porting, testing the clock driver along with refactoring the Beagle i2c driver.

As per feedback from my mentor, I posted my patches to the mailing list and spent a fair amount of time discussing and incorporating the changes suggested.

Outcomes of phase 2:

  1. Tested the pinmux driver with libBSD.
  2. Ported the clock driver into RTEMS.
  3. Fixed bugs in the clock driver.
  4. Tested the clock driver with libBSD.
  5. Refactored the Beagle i2c driver.

Phase Three

In this phase, we realized the license issue with FreeBSD OFW API. The OFW API in FreeBSD was BSD-4 licensed and RTEMS only allows BSD-2 licensed code. This wasn’t previously noticed because RTEMS imports a lot of code from FreeBSD so the licensing part was ignored :(. This was discussed in the mailing list and it was decided to implement the OFW API in RTEMS itself. So I proceded with implementing the OFW API in RTEMS. Wrote a simple test for it. Extended it with few more functions which would be beneficial while writing drivers. Added compatibility for FreeBSD, tested the OFW API with libBSD after removing the FreeBSD OFW API from libBSD. And also spent some time fixing bugs in the implementation. Finally, the last few days were spent in refactoring the previous patches to this API, fixing bugs and writing blogs.

Outcomes of phase 3:

  1. Implemented the RTEMS OFW API.
  2. Tested with libBSD
  3. Refactored the previous patches.
  4. Updated the blogs.
  1. Pinmux driver

  2. Implement FreeBSD structures in RTEMS

  3. Clock driver
  4. OpenFirmWare API
  5. Refactored i2c driver
  • The below mentioned branches contain all the commits that were made through out GSoC, using these branches will make your testing easy :).

Future Work

I wasn’t able to refactor all the drivers, so I will be refactoring these drivers and will work on unifying the BSP.

Acknowledgment

I thank my mentors and all the members of the RTEMS community for being really supportive, it was an excellent learning experience and a lot of fun.