Accessing GPIO and PWM on BeagleBone AI

Question

I'm running through the BeagleBone examples for the AI, but the ones that attempt to read or write to pins throw errors in both Python and bonescript.

Here is the output from analoginout.js:

Hit ^C to stop

info: No pinmux for P9_14

fs.js:733

var r = binding.read(fd, buffer, offset, length, position);

^

Error: ETIMEDOUT: connection timed out, read

at Error (native)

at Object.fs.readSync (fs.js:733:19)

at tryReadSync (fs.js:488:20)

at Object.fs.readFileSync (fs.js:528:19)

at Object.readAIN (/usr/local/lib/node_modules/bonescript/src/hw_mainline.js:287:30)

at Object.f.analogRead (/usr/local/lib/node_modules/bonescript/src/index.js:330:19)

at Timeout.loop [as _onTimeout] (/var/lib/cloud9/BeagleBone/AI/analogInOut.js:23:19)

at ontimeout (timers.js:386:11)

at tryOnTimeout (timers.js:250:5)

at Timer.listOnTimeout (timers.js:214:5)

Is there a config I need to do first? I see other's in the world with this issue on older BeagleBone's and the responses vary considerably.

This is the code:

const b = require('bonescript');


const inputPin  = "A3";
const outputPin = "P9_14";


console.log('Hit ^C to stop');
b.pinMode(outputPin, b.ANALOG_OUTPUT);
setTimeout(loop, 200);  // work-around to wait for PWM permissions


function loop() {
    var value = b.analogRead(inputPin);
    process.stdout.write(inputPin + '-->' + outputPin + ': ' + (value*100).toFixed(1) + '%   \r');
    b.analogWrite(outputPin, value);
    setTimeout(loop, 10);
}

Thanks,

Sean

const inputPin = "A3";
const outputPin = "P9_14";

console.log('Hit ^C to stop');
b.pinMode(outputPin, b.ANALOG_OUTPUT);
setTimeout(loop, 200); // work-around to wait for PWM permissions

function loop() {
 var value = b.analogRead(inputPin);
 process.stdout.write(inputPin + '-->' + outputPin + ': ' + (value*100).toFixed(1) + '% \r');
 b.analogWrite(outputPin, value);
 setTimeout(loop, 10);
} Thanks, Sean

Sean_Miller · Accepted Answer

After two weeks and 20+ hrs of research, I'm calling this chicken done. Here's the summary: BeagleBone AI Survival Guide V3.18: PWM, I2C, Analog/Digital Read/Write, Vision AI, Video Text Overlays, Audio, & Hardware

Sean_Miller · Answer

I saw these two references tonight in my hunt. My thoughts were "this surely is handled in by the bonescript and Python libraries on the fly, right?" "Otherwise, it would be in the comments in the header, right?" I guess not. For the video, I didn't have the directories he showed for the capes and trees. I tried the redirect to export tricks, but still received the same error of having no pinmux. I'll run it harder through the paces tomorrow evening. I found the tutorials just aren't out there like you find for Raspberry Pi and Arduino IDE driven microcontrollers. But, so, far, I love the idea of computations happening at the speed of the frame with the tidl libraries, love the Cloud 9 interface (1st time using it), and love being able to use it as an adhoc device while its connected to the internet. Just got to get an LED to blink and stop it from calling my black cat a ping-pong-ball. -Sean

mp2100 · Answer

Sean, I am definitely not a nodejs expert, but I compared your code to the example from cloud9 on my BBBlack (I don't yet have a BB AI). In the given example, the first 3 lines read: var b = require('bonescript'); var inputPin = "P9_38"; var outputPin = "P9_14"; Your code reads: const b = require('bonescript'); const inputPin = "A3"; const outputPin = "P9_14"; Is there a reason you used constant instead of variable?

mayermakes · Answer

The only thing I could find out about this issue is that the device tree files for the BB-AI are missing, there is currently no suitable file provided for the BB-AI all the BBB black files just brick the BB-Ai if loaded with uENv.txt. the Universal cape also does not support the processor. I raised an Issue on the github for the examples and messaged them,. hope Beaglebone will shortly provide a suitable overlay file /inlcuded it loaded in the next OS image release. thanks for posting your solution! For generall usage these setup procedures should be handeled in a Library or the u-boot (like intended). To get an urgent project working i had to do some workaround which thought me about interfacing it with USB devices, but I really would like to redo it without any additional hardware.

mp2100 · Answer

I assume you can un-brick it by putting the debian image for the BB AI onto an SD card and boot from there. (and reflash the eMMC if you want to)

clem57 · Answer

#include #include using namespace std; int main() { FILE *export_file = NULL; //declare pointers FILE *IO_direction = NULL; FILE *IO_value = NULL; char str1[] = "0"; char str2[] = "1"; char str3[] = "out"; char str[] = "23"; //this part here exports gpio23 export_file = fopen ("/sys/class/gpio/export", "w"); fwrite (str, 1, sizeof(str), export_file); fclose (export_file); //this part here sets the direction of the pin IO_direction = fopen("/sys/class/gpio/gpio23/direction", "w"); fwrite(str3, 1, sizeof(str3), IO_direction); //set the pin to HIGH fclose(IO_direction); usleep (1000000); for (int i=0; i<10; i++){ //blink LED 10 times IO_value = fopen ("/sys/class/gpio/gpio23/value", "w"); fwrite (str2, 1, sizeof(str2), IO_value); //set the pin to HIGH fclose (IO_value); usleep (1000000); //delay for a second IO_value = fopen ("/sys/class/gpio/gpio23/value", "w"); fwrite (str1, 1, sizeof(str1), IO_value); //set the pin to LOW fclose (IO_value); usleep (1000000); //delay for a second } } The 3 bold lines are the setup for pin 23.

Sean_Miller · Answer

Jason Kridner has released a beta for the BBAI GPIO libraries for node.js: https://groups.google.com/forum/embed/?place=forum%2Fbeagleboard&showsearch=true&showpopout=true&showtabs=false&hideforu… I'm try to get something going tomorrow. He also released an update that was to fix the tidl examples, but that one went backwards on me and now I can't get it to execute without error. It's been posted to his support forum. -Sean

Sean_Miller · Answer

Here's a better link to Jason's post: https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/beagleboard/0G2Ivf9lQeA/gSaCajE4CAAJ

Sean_Miller · Answer

And another pin hack for the BBAI for Adafruit's Python Library BBB pins:

out = "P8_13" #actually 8_22 on BBAI

Here's how I'm finding it...

At the terminal type:
- node -pe "require('bonescript').bone.getPinObject('p8.22').ai.gpio"
It will give you a number. In this case it returns 23.
Do a CTRL f on the number here: https://github.com/adafruit/adafruit-beaglebone-io-python/blob/master/source/common.c#L73
For this one, I found { "EHRPWM2B", "P8_13", 23, 4, -1} - which is P8_13.

So, using BBB's reference to P8_13 will get you use of BBAI 8_22.

Two out pins are much better than none for now. Now to get an analog in and a PWM out working. Most likely, as soon as I get it, Adafruit will release their update.

Sean_Miller · Answer

Dude, I've been cobbling everything I can across a very quiet internet on this topic. Coming in cold to the BeagleBone platform, I've got a good 15 hours of research since I first posted this. So, as soon as I find something that makes an LED blink, I zap it here so others don't have to lose the time concocting hacks to get their projects going. I'm not taking credit for inventing the internet, just showing others how to get their LEDs to blink. Users here are always cool and helpful and I enjoy their conversation - e14 is my version of Facebook. Click "show earlier" and you will find links to every thread I'm monitoring bright and clear. I hope others monitor them as well and translate them to simple solutions that a dumb guy like me can understand. -Sean

clem57 · Answer

Yes since the number of pins is less than possible interfaces... https://www.bing.com/videos/search?q=how+to+setup+pins+beagle+bone&docid=608009253376952439&mid=30773886A1337BD47A863077… Or a better read https://vadl.github.io/beagleboneblack/2016/07/29/setting-up-bbb-gpio . Enjoying the BB-AI Sean_Miller ?

Sean_Miller · Answer

My code came from the example code found in the Cloud9 IDE under cloud9-->BeagleBone--AI which is on the BeagleBone GitHub as well. https://github.com/beagleboard/cloud9-examples/tree/master/BeagleBone/AI As for const versus var, in general, I do prefer const for a variable I don't want to mistakenly change its value, as in this case. I want to set it and fix it to that pin for all references. See ya', Sean

Sean_Miller · Answer

I got excited when I read this article on Adafruit: https://learn.adafruit.com/introduction-to-the-beaglebone-black-device-tree/overview But then I read your post that the BeagleBone Black overlays will brick the AI. Oh well, at least I understand it now, just not enough to make my own overlay. See ya', Sean

Sean_Miller · Answer

Found a link that looks promising on establishing GPIO pins: https://www.elinux.org/EBC_Exercise_41_Pin_Muxing_for_the_AI However, I simply bricked mine when I tried it. -Sean

clem57 · Answer

Sean_Miller -> So the AM5X vs AM335 requires overlays for the DTB not be done in user-space. Therefore they are done at boot time. Take a look at this discussion for the details. https://groups.google.com/forum/embed/?place=forum%2Fbeagleboard&showsearch=true&showpopout=true&showtabs=false&hideforu… Clem

Sean_Miller · Answer

Thanks, Clem. I am definitely in unfamiliar territory here. If I can get analog in and PWM out on top of P9.15 being a digital out, I'll be in business. After installing the new BoneScript library for the AI, Jason has you type this at the command line: node -pe "require('bonescript').bone.getPinObject('p9.15').ai.gpio" I don't know the background of this, but I did find that the demo worked after a reboot without having to type it again. I tried it with P9.16, but it did not light up when ran. No error, just didn't light up. I wonder what the other folks that received the BBAI are doing in the GPIO arena. I hope they chime in. The topic seems oddly quiet even on the BB Forum. Based on the view count on the topic, I've been almost all of them. This is surprising with the stats this thing will be capable of. -Sean

Sean_Miller · Answer

Here's a hack for Python on the BBAI.

Change...

out = "P9_15"

to

out = "P8_39"

in the blink demo and you'll get an LED blink. It's because of the mapping difference between the BBB and BBAI.

See ya',

Sean

Sean_Miller · Answer

Some work by Jason Kridner was just updated on github for BBAI GPIO and the UBoot process: https://github.com/beagleboard/beaglebone-ai/tree/master/SW when I run sudo apt update, it doesn't show anything to update. Anyone know how to integrate these changes (pasted below)? -Sean * Disable all UART TX pins (switch to GPIO) * Disable SPI3 (switch to GPIO) * Disable eHRPWMs (switch to GPIO) * Match power-on pull-up/down status where possible * Enable GPIOs on alternate pins (ie., other shorted pin is PRU input, UART RX, eQEP, etc.) * Enable GPIOs for all pins not otherwise enabled * On eQEP shorted pins, pull-down on eQEP and no-pull on GPIO * On UART/PRU shorted pins, pull-down on GPIO and no-pull on UART/PRU * Add pull-downs on UART-only pins (console) * Correct voltages for vddshv1 and vddshv7 (3.3V)

Sean_Miller · Answer

Yes, creating a new image unbricked it. It's definitely what I did attempting to set the device tree that cause the corruption. See ya', Sean

jomoenginer · Answer

Again, your "node -pe "require('bonescript').bone.getPinObject('p8.22').ai.gpio"" command came from a Jason post regarding an issue with the node.js lib. The bonescript gave you 23 since P8_22 on a BB AI is mapped to gpio1_23 thus it is like ((32x0) +23) = gpio 23. Also, by default, the unused pins tend to be set to a default that seems to set it to the GPIO mode, mode 14. To set the pin to PWM, it would need to be set to Mode 10 to enable ehrpwm3B. Jason sent out a table but this is listed in the TI AM572x Data sheet as well: http://www.ti.com/lit/ds/symlink/am5728.pdf To make this change, from what I gather from Robert, the pin would need to be set to the following in the am5729-beagleboneai.dts Ex: DRA7XX_CORE_IOPAD(0x3794, PIN_OUTPUT | MUX_MODE10) /* AC8: P8.23: mmc3_dat4.ehrpwm3A - PWM3A */ Changes to the .dts require a rebuild of the dtb: cd /opt/source/dtb-4.19-ti/
make src/arm/am5729-beagleboneai.dtb 
sudo make install
sudo reboot NOTE: The pin will not work as normal GPIO output at this point. Since the Adafruit stuff is not really working with the BB AI, I'm still looking for an example to test the PWM capability.

jomoenginer · Answer

It should work with either kernel, but I have only used 4.19. I have done all of the latest updates and pulled in the latest code changes as well. After changing the pin mode, the analogInOut.js example no longer works so I suspect I am still missing something. It does sort of work with the pin as a GPIO, but only as an on or off state and does not fade the LED. However, 4.19 seems to break the TIDL example where it will not build anymore and the blinkLED.js example causes the system to become nearly unresponsive. Another thing I found with the Cloud9 examples is that you need to set the gpio port before running the scripts. Ex for P8_23 set as GPIO (Mode 14): echo 22 > /sys/class/gpio/export 
echo out > /sys/class/gpio/gpio22/direction I also removed the other led except usr3 since I still want to see the heartbeat on the board. . const leds = ["USR3", "P8_23"];
//const leds = ["USR0", "USR1", "USR2", "USR3", "P9_15"]; The board does not seem to become unresponsive after running the example this way.

Accessing GPIO and PWM on BeagleBone AI

Top Replies