Interruptions in BBB

General Discussion
1

Hi everyone,

I am migrating from another platform (IoT) to a BBB, in that other device I had an interruption through a “timer” which was executed every 200us, a very precise interruption (±2us max measured with an oscilloscope) that the only thing I did was monitor the states of the digitals, a timer was used due to the little precision that handling each digital through external interruption gave us.
My initial questions are:

1.- How are timers managed in BBB? Does anyone have any idea of the accuracy?
2.- How efficient are the external interruptions?

I plan to use Cloud9 with the BoneScript library

2

Forget about interrupts!

The BBB CPU includes two real-time units called PRU. Use ASM code to poll the digitals in the required timing (±0us). A 200 us loop is 1000 PRU cycles.

Regards

3

Thanks @DTJF, looking some examples (cloud9-examples/BeagleBone/Black/pru at master · jadonk/cloud9-examples · GitHub) i saw that the PRU can work like my previous development (and better than this one), but I don’t have any idea about how to do that. That is to say, in my previous development when the timer fulfilled the established time it made a call to a function that verified the state of +20 digitals, does it possible to do using the PRU? do you know any example to configure the PRU like this way?

Kind Regards

4

Hi @Fredd ,

what I always does is working with the internal timer of the pru.(https://community.element14.com/products/devtools/single-board-computers/next-genbeaglebone/b/blog/posts/beaglebone-pru---timer-functionality)
The internal PRU cycle is 5ns so you need to sum the current timer value + loop timer and inside the loop control the comparison of the current timer value X your variable.

5

Hi @Juvinski,

Thanks for your support, reviewing the example I understood that the PRU (correct me if I’m wrong) must be programmed independently of the CPU, if so, how is it possible to communicate the PRU with CPU programming?

6

Hi @Fredd

there is a shared memory between PRU and CPU
I recommend the excellent PRU Cookbook PRU Cookbook

7

Hi @Juvinski,
Thank you very much, I will continue documenting myself to learn more about the PRU that I see is one of the best ways.

Kind Regards

8

@Fredd ,

Seth here. The book, both versions, have specific files and background docs. all dedicated to the chip in question.

I can try to post the how to port the PRUSS TI docs. if I can scramble and find them. It may be of some interest…

Now, things change and I am sure some of it is still relevant but I will post the files on Youtube.com if I am allowed to do so.

Seth

Update

I have only Sitara Bootcamp files leftover. They are PPS…I thought I could still find the files.

I am sorry. I may still have the PRU Docs. in case they are difficult to track down. I will need to open some files I have not seen in some time. Get ready! Okay and so…

  1. I found some files from the past but some may not be able to be witnessed. I have no clue as to how to handle things but I found some preliminary material on some old 'puters.
    a. PRU Read Latencies (Rev. A) (ti.com)
    b. Updates to that may have taken place since then…
    c. I will contact someone to see if sharing is allowed from me.
  2. PRU Assembly Instruction User Guide
    a. I am kind of bouncing around now…
    b. My PRU Expertise is not concrete…
    c. Enjoy!
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