Final: GPIO Checkpoint

33. Final: GPIO Checkpoint#

For this checkpoint, you must prove that you can trigger an action in Docker by driving a GPIO pin to digital HIGH.

33.1. Deliverables#

  1. Conduct a BLERP analysis for voice recording and transcription.

  2. Prove that you can use the GPIO to trigger a simple action in Docker running Python, such as printing to the screen.

Hint

  1. Check the GPIO on the Jetson host, with Bash, and with no Docker

  2. Then do the Python in Docker

33.2. Jetson GPIO with Bash#

Before you try to do anything with Docker and Python, make sure your 40-pin GPIO header works.

TLDR:

Put \(0V\) on pin 29 then run this line in the terminal:

# With 0V on pin 29
# Will print 0 to terminal, for digital LOW
gpioget gpiochip0 105

Now put \(3.3V\) on pin 29 then run the line again

# With 3.3V on pin 29
# Will print 1 to terminal, for digital HIGH
gpioget gpiochip0 105

Explanation#

Your Jetson has two headers. The one we care about is named gpiochip0, which is the 40-pin vertical header.

According to JetsonHacks: NVIDIA Jetson Orin Nano GPIO Header Pinout, pin #29 on is named GPIO01. However, the OS uses the Sysfs lines that map to the system on a chip (SoC) spec. So GPIO01 is actually referred to as line 105.

On your Jetson you can run this to get the SoC name for line 105, which is GPIO01, which is pin #29 🤪

# Find name for GPIO01
gpioinfo | grep 105
# line 105: "PQ.05" unused input active-high

Cool, so we will simply call pin #29 line 105 but we now know it’s configured as active-high input to the SoC port “PQ.05”.

Note

This is actually super similar to the .xdc constraints file for the Basys3 board in ECE 281!

Now we can read the digital value on the pin!

# Should print 0 or 1 to the terminal
gpioget gpiochip0 105

I typed gpio and then pressed tab, tab to find gpiomon.

gpiomon --help

Looks like there are some flags to process something on the first rising edge. Nice!

# Run echo on rising edge
gpiomon -r -n 1 gpiochip0 105 | while read line; do echo "event $line"; done

Disclaimer: I never would have figured this out without ChatGPT https://chatgpt.com/share/67d4a6d8-5920-8003-a93a-67c68b6acc8c but notice how much research I did first in order to ask the right questions! Also, not all the files it pointed me towards exist.

33.3. Jetson.GPIO in Docker#

We can use the Python NVIDIA/jetson-gpio library in combination with libgpiod to access the Jetson’s GPIO in Python.

Important

When you run a container that you want to access the GPIO you must allow it to access the device, so add this flag after docker run

--device=/dev/gpiochip0

Setup#

You can do this interactively with a running container, but you can (and should) bake it into a Dockerfile!

First install gpiod (this provides the command line tools such as gpioget)

apt install gpiod

Next, install the Jetson GPIO Python library.

pip install Jetson.GPIO

Tell the library which Jetson model it’s running via an environment variable:

# In terminal
export JETSON_MODEL_NAME=JETSON_ORIN_NANO

or

# In Dockerfile
ENV JETSON_MODEL_NAME=JETSON_ORIN_NANO

Run Test Script#

Once setup, run Python.

'''Prints 'UP' or 'DOWN' based on edges on Jetson pin #29'''
import Jetson.GPIO as GPIO

# Init as digital input
my_pin = 29
GPIO.setmode(GPIO.BOARD)  # BOARD pin-numbering scheme
GPIO.setup(my_pin, GPIO.IN)  # digital input

print('Starting Demo! Move pin 29 between 0V and 3.3V')

while True:
    GPIO.wait_for_edge(my_pin, GPIO.RISING)
    print('UP!')
    GPIO.wait_for_edge(my_pin, GPIO.FALLING)
    print('down')
Contents