EBC Exercise 30 PRU via remoteproc and RPMsg

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thumb‎ Embedded Linux Class by Mark A. Yoder

Here's how to setup a Bone to play with the PRUs using remoteproc and RPMsg. My goals here are:

  1. Everything compiles on the Bone.
  2. The PRUs are programmed in 'C', not assembly.
  3. remoteproc and RPMsg are used.

A good starting place on the TI site for PRUs is http://processors.wiki.ti.com/index.php/PRU-ICSS. PRU_Training:_Hands-on_Labs has some good hands on labs, however they are all based on Code Composer Studio and I want my examples to compile and run on the bone.

Chapter 13 of Derek's Molloy's excellent Exploring BeagleBone gives many good examples of using the PRU, but he uses the older UIO interface. I want to use the new remoteproc and RPMgs.

ZeekHuge has some nice Bone-based examples that that are remoteproc and bone-compile based, so that's what I start with here.

But first, you need to get your bone set up.


To start, I'm running with:

bone$ cat /ID.txt
BeagleBoard.org Debian Image 2016-06-19
bone$ uname -a
Linux yoder-debian-bone 4.4.12-ti-r32 #1 SMP Wed Jun 22 20:18:35 UTC 2016 armv7l GNU/Linux

You need to be running at least 4.4.12-ti-r32 for these examples to work [1].

Disable the HDMI

The PRUs have direct access to many pins that are also used by the HDMI. Check to see if the HDMI has been disabled.

bone$ config-pin -q P8_45
P8_45 pinmux file not found!
cape-universala overlay not found
run "config-pin overlay cape-universala" to load the cape

If you get the message above, you need to disable your HDMI. Do it by editing /boot/uEnv.txt and uncommenting the following by removing the # in front of the dtb line:

##BeagleBone Black: HDMI (Audio/Video) disabled:

Note the name of the file is am335x-boneblack-emmc-overlay.dtb, we'll use this later. Then reboot and try again.

bone$ config-pin -q P8_45
config-pin -q P8_45
P8_45 Mode: default Direction: in Value: 0

Good the HDMI is now disabled. Later we'll use config-pin to set pins to the PRU.

Setting up the PRU compiler

The PRU compiler should already be installed.

bone$ which clpru

If not, you'll have to search around to learn how to install it. (Beyond the scope of this page.)

However some setup must be done so it can find all the libraries it needs.

bone$ export PRU_CGT=/usr/share/ti/cgt-pru
bone$ export PRU_SUPPORT=/opt/source/pru-software-support-package
bone$ cd $PRU_CGT
bone$ mkdir -p bin
bone$ cd bin
bone$ ln -s `which clpru`  .
bone$ ln -s `which lnkpru` .

The variable PRU_CGT is used by the Makefiles and scripts to know which compiler to run. I suggest you put export PRU_CGT=/usr/share/ti/cgt-pru in your .bashrc file so it's set every time you login. The other commands only need to be run once.

Making sure remoteproc is running

If you are running 4.4.14-ti-r34 or later you have to enable remoteproc. Check for remoteproc with:

bone$ lsmod | grep pru
pru_rproc              13507  0 
pruss_intc              7451  1 pru_rproc
pruss                  10611  1 pru_rproc

If you get the response above, remoteproc is running and you can skip the rest of this section. If not, follow these instructions from [2] to enable it.

Edit your device tree

bone$ cd /opt/source/dtb-4.4-ti 
bone$ nano src/arm/am335x-boneblack-emmc-overlay.dts 

Where am335x-boneblack-emmc-overlay.dtb is the file you remembered from above.

Now change:

/* #include "am33xx-pruss-rproc.dtsi" */ 


#include "am33xx-pruss-rproc.dtsi"


bone$ make
bone$ make install

Create blacklist and reboot

bone$ echo "blacklist uio_pruss" > /etc/modprobe.d/pruss-blacklist.conf
bone$ reboot 
bone$ lsmod | grep pru
pru_rproc              13507  0 
pruss_intc              7451  1 pru_rproc
pruss                  10611  1 pru_rproc

Now remoteproc is running.

Installing Examples

I've found some examples that are a good starting point.

TI's examples

The examples from TI's site [3] are already on the bone, but let's make them easier to find.

bone$ mkdir pru
bone$ cd pru
bone$ ln -s /opt/source/pru-software-support-package .
bone$ cd pru-software-support-package

The first lines makes a directory for keeping all your PRU file and the last commands link to the already loaded files and changes to the directory. Look around and see what's there. Be sure to checkout the ReadMe.txt file.

bone$ cat ReadMe.txt
Programmable Real-time Unit (PRU) Software Support Package release 5.0


  The PRU Software Support Package is an add-on package that provides a framework 
  and examples for developing software for the Programmable Real-time Unit 
  sub-system and Industrial Communication Sub-System (PRU-ICSS) in the supported 
  TI processors.  The PRU-ICSS achieves deterministic, real-time processing, direct 
  access to I/Os and meets ultra-low-latency requirements. 

  This software package contains example PRU firmware code as well as application 
  loader code for the host OS. The examples demonstrate the PRU capabilities to 
  interact with and control the system and its resources.

  For more details about the PRU, visit 


  This package includes the following resources:

       ---------	--------
       examples 	Basic PRU examples
       include 	PRU firmware header files
       labs 		Source code for step-by-step labs
       lib 		PRU library files and library source files
       pru_cape 	Demo software for the BeagleBone PRU Cape


  For more information about the PRU, visit:

       PRU-ICSS Wiki		http://processors.wiki.ti.com/index.php/PRU-ICSS
       PRU Training Slides	http://www.ti.com/sitarabootcamp
       PRU Evaluation Hardware	http://www.ti.com/tool/PRUCAPE
       Support			http://e2e.ti.com


ZeekHuge has a Google Summer of Code (GSoC) 2016 project called BeagleScope that has some very nice working examples. We'll look at these in more detail. Clone a copy of your own.

bone$ cd pru
bone$ git clone https://github.com/ZeekHuge/BeagleScope.git
bone$ cd BeagleScope
bone$ cat README.md
What is BeagleScope ?
The project, as the part of GSoC-2016, aims to provide with software support to deploy the 
PRUSS subsystem on AM33xx processors, as a fast and parallel data acquisition units.
The PRU cores being highly optimized for I/O operations and single cycle instruction 
execution (mostly), are an appropriate choice for bit-banging and offloading tasks. 
BeagleScope uses this very feature of PRUs to offload the parallel data transactions 
and fast data acquisition.

Run examples

BeagleScope examples

Now that you have everything setup, it's easy to run the BeagleScope examples.

bone$ cd BeagleScope
bone$ cd docs
bone$ ls
BBB-ADC.pdf                       clpru_and_C_usage.notes
BeagleboneBlackP8HeaderTable.pdf  current_remoteproc_drivers.notes
BeagleboneBlackP9HeaderTable.pdf  Introductory_slides.pdf

Look around. The docs directory has some good documentation. The BeagleboneBlackP*HeaderTable.pdf files tell where the PRU registers appear on the headers.

P8 Header PRU pins

Blinky example

Here's how to blink an LED wired to P8_45.

bone$ cd BeagleScope/examples/firmware_exmples/pru_blinky
bone$ ./deploy.sh

This will run make and then install the code on the PRU and start it running.

This must be compiled on the BEAGLEBONE BLACK itself
It was tested on 4.4.12-ti-r31 kernel version
The source code for blinky ie PRU_gpioToggle was taken from
pru-software-support-package and can be cloned from
git clone git://git.ti.com/pru-software-support-package/pru-software-support-package.git
******NOTE: use a resistor >470 ohms to connect to the LED, I have alredy made this mistake.
To continue, press any key:
-Placing the firmware
-Configuring pinmux
P8_45 Mode: pruout
Rebooting pru-core 1
Done. Blinky must be up on pin P8_45

Your LED should be blinking now. Look in deploy.sh to see how the code is loaded on PRU 1 and started running.

Now go explore the other examples. There is much to be learned.


Debugging realtime can be a challenge. I've found a good start on a PRU debugger at https://sourceforge.net/projects/prudebug/files/latest/download. I've copied the code to github and made some simple changes. (Original version uses word addresses and which I switched to byte addresses to the addresses match the output of the linker.)

thumb‎ Embedded Linux Class by Mark A. Yoder