GPIO function test of NVIDIA Jetson

Keywords: Deep Learning Jetson

0 background

The Jetson TX1, TX2, AGX Xavier and Nano development boards contain a 40 pin GPIO connector, similar to the 40 pin connector in Raspberry Pi. NV officially gives a GPIO library, which is a Python version, and   The RPi.GPIO Library of Raspberry Pi is the same. This paper introduces the content and usage of the library.

1 installation method

It can be installed directly through pip

sudo pip install Jetson.GPIO

Download sample code

git clone

In the Jetson GPIO project

  1.   The lib/python path contains Python modules that implement all library functions. module is the main component that will be imported into the application and provide the required API, and and is referenced by and cannot be called directly by applications
  2. The samples path lists some application examples. The specific meanings are as follows
  • this application uses the BCM pin numbering mode and reads the value at pin 12 of the 40 pin connector and prints the value to the screen.

  • this application uses the BCM pin numbering mode of Raspberry Pi and outputs alternating high and low values on BCM pin 18 (or BOARD pin 12) every 2 seconds.

  • this application uses the BOARD pin number. It requires a button connected to pin 18 and GND, a pull-up resistor connecting pin 18 to 3V3, and an LED and current limiting resistor connected to pin 12. The application reads the button status and keeps the LED on for 1 second at a time, and the button is pressed.

  • this application uses the BOARD pin number. It requires a button connected to pin 18 and GND, a pull-up resistor connecting the button to 3V3, and an LED and current limiting resistor connected to pin 12. The application executes with a has the same function, but performs blocking and waiting for button press events instead of constantly checking the value of the pin to reduce CPU utilization.

  • this application uses the BOARD pin number. It requires a button connected to pin 18 and GND, a pull-up resistor connecting the button to 3V3, an LED and current limiting resistor connected to pin 12, and a second LED and current limiting resistor connected to pin 13. The application flashes slowly. Only when the button is pressed, the first LED flashes continuously and quickly, and the second LED flashes 5 times.

2 API functions

2.1 setting mode

For Jetson series boards, we need to set the mode to BOARD. We don't care about other modes


You can use the method below to get whether the setting is successful

mode = GPIO.getmode()

  The results will be gpio.board, gpio.bcm, gpio.cvm and gpio.tegra_ One of SOC or None  

2.2 input pin

Before calling the gpio pin, the first step is to define the input or output direction.

Set pin to input direction

GPIO.setup(channel, GPIO.IN)

Among them, channel is the specific pin number, such as 30, 25, etc

Read the input value of the pin

state = GPIO.input(channel)

The return value is GPIO.LOW or GPIO.HIGH, i.e. low signal or high signal

2.3 output pin

Set pin to output direction

GPIO.setup(channel, GPIO.OUT)

It is also supported to specify whether the default output is high or low

GPIO.setup(channel, GPIO.OUT, initial=GPIO.HIGH)

Of course, it also supports setting the direction of multiple pins at the same time, such as

channels = [18, 12, 13]
GPIO.setup(channels, GPIO.OUT)

After definition, set the output value of the pin to support multiple modes

channels = [18, 12, 13] # or use tuples
GPIO.output(channels, GPIO.HIGH) # or GPIO.LOW
# set first channel to HIGH and rest to LOW
GPIO.output(channel, (GPIO.LOW, GPIO.HIGH, GPIO.HIGH))

2.4 inspection direction

You can use the interface below to check whether a pin is an input pin or an output pin


  The return value is   GPIO.IN or   GPIO.OUT

2.5 clear pin function

After the program runs, it is best to have a clear operation to restore the pin to the default state


If you do not want to clear the status of all pins, you can also choose to clear the specified pins

GPIO.cleanup(chan1) # cleanup only chan1
GPIO.cleanup([chan1, chan2]) # cleanup only chan1 and chan2
GPIO.cleanup((chan1, chan2))  # does the same operation as previous statement

3 interrupt function

When monitoring the status of input pins, in order to prevent non-stop polling and occupying cpu resources, API provides three interfaces to improve

3.1 wait_for_edge()

This function blocks the calling thread until the provided edge is detected, such as

GPIO.wait_for_edge(channel, GPIO.RISING)

The second parameter represents the change signal to be detected and supports    GPIO.RISING, GPIO.FALLING or GPIO.BOTH, and rising edge trigger, falling edge trigger or both. In addition, the timeout can be set

# timeout is in milliseconds
GPIO.wait_for_edge(channel, GPIO.RISING, timeout=500)

The return of the function is the detected signal, or it returns None after timeout

3.2 event_detected()

This function can be used to periodically check whether events have occurred since the last call. This function can be set and called as follows

# set rising edge detection on the channel
GPIO.add_event_detect(channel, GPIO.RISING)
if GPIO.event_detected(channel):

Similarly, several trigger modes such as rising edge, falling edge or rising and falling edge are also supported

3.3 callback function

The callback function is executed in the new thread, so the main program and callback function can run concurrently to respond to events, such as

# define callback function
def callback_fn(channel):
    print("Callback called from channel %s" % channel)

# add rising edge detection
GPIO.add_event_detect(channel, GPIO.RISING, callback=callback_fn)

You can also specify multiple callback functions

def callback_one(channel):
    print("First Callback")

def callback_two(channel):
    print("Second Callback")

GPIO.add_event_detect(channel, GPIO.RISING)
GPIO.add_event_callback(channel, callback_one)
GPIO.add_event_callback(channel, callback_two)

However, it should be noted that multiple callback functions will be executed sequentially rather than simultaneously, which is related to the threading mechanism of python. To prevent multiple calls to the callback function by multiple events, you can choose to set the de dithering time:

# bouncetime set in milliseconds
GPIO.add_event_detect(channel, GPIO.RISING, callback=callback_fn,

If you do not need to detect changes, you can use the clear function


4 PWM function

samples/ shows how to use PWM function. There are two points to note:

(1) Not every development board has PWM function. Jetson Nano supports 2 PWM channels and Jetson AGX Xavier supports 3 PWM channels. Jetson TX1 and TX2 do not support any PWM channels.

(2) The jetson board does not turn on the PWM function by default. It needs to be configured with the jetson IO tool to enable the PWM function. Refer to< NVIDIA Jetson SPI function enable >Make settings

5 C + + interface

In addition to the official Python interface, there is also the GPIO API of C + + interface. The functions are the same as those of python, the use method is similar, and the installation method is the same

git clone
cd JetsonGPIO/build
make all
sudo make install

Compilation method

g++ -o your_program_name your_source_code.cpp -lpthread -lJetsonGPIO

The API interface implementation methods described above will not be repeated here, but can be viewed directly Project description that will do

Posted by stuffradio on Sat, 06 Nov 2021 01:30:45 -0700