BBAI - PRU Pin Question

thechef · March 22, 2023, 12:12pm

Been going over as many PRU examples I can and there is one core question I have.

In the example from the Cloud9 Example folder

beagleboard/cloud9-examples/blob/summer2021/BeagleBone/AI/pru/blinkExternalLED.pru1_1.c

////////////////////////////////////////
//	blinkExternalLED.c
//	Blinks one LED wired to P9_25 by writing to memory using the PRU
//	Wiring:	P9_25 connects to the plus lead of an LED.  The negative lead of the
//			LED goes to a 220 Ohm resistor.  The other lead of the resistor goes
//			to ground.
//	Setup:	Set the direction to out on P9_25
//	See:	prugpio.h to see to which ports the P8 and P9 pins are attached
//	PRU:	pru1_1
////////////////////////////////////////
#include <stdint.h>
#include <pru_cfg.h>
#include "resource_table_empty.h"
#include "prugpio.h"

volatile register unsigned int __R30;
volatile register unsigned int __R31;

void main(void) {
	// Points to the GPIO port that is used

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This uses P9_25 as a PRUOUT

However according to the github system reference manual

github.com

jadonk/beaglebone-ai-wiki/blob/master/System-Reference-Manual.asciidoc

= BeagleBone AI System Reference Manual
:toc: preamble

image:images/BB_AI_BeautyAngle_800px.jpg[BeagleBone AI Beauty Angle]

TODO: Update image

[[this-document]]
*THIS DOCUMENT*

image:images/cc-by-sa-88x31.png[Creative Commons CC-BY-SA]

This work is licensed under a
http://creativecommons.org/licenses/by-sa/4.0/[Creative Commons
Attribution-ShareAlike 4.0 International License]

All derivative works are to be attributed to
https://beagleboard.org/about/jkridner[Jason Kridner of
BeagleBoard.org].

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P9_25 isn’t even accessible to PRU1 at all. it would have to be on PRU2.

But I will admit, compiling it somehow works and it blinks. This is all done on the 4.14 image.

I moved to the latest nightly builds which don’t have the cloud9 stuff but rather vscode. The example no longer works however got it to compile. I assume this is something due to the beaglebone-ai.dts changing over time.

Am I completely missing some core concept?

gomer · March 22, 2023, 2:18pm

there is no PRU2. According to documentation that you cited, P9_25 is on PRU1 of PRU-ICSS2.

Assume that the SRM is correct … 6.12.5 PRU-ICSS2 Pin Access

this section has 3 hits for P9_25:

pr2_pru1_gpo5
pr2_pru1_gpi5
pr2_mii1_col

if you accept their naming convention, P9_25 is on ‘pr2’ NOT ‘PRU2’. more specifically, it is on PRU1 of PR2.

(I think that) The cloud9 file (comment) may need to be updated.

I suspect that close examination of this file will be more accurate than the comments.

good luck
gomer

thechef · March 22, 2023, 2:55pm

Ah thanks so much. I was jumping to my own wrong conclusion on the naming convention of the PRU vs PR which you have cleared up.

Really though was just staring too long thank you!