jetson-tx1-gpio-pins.md

Programmatic control over GPIO pins on the Jetson

There are many guides out there that give bits and pieces of information about how to control the GPIO output on the Jetson but none give a mapping between the physical pin number and the Broadcom or BCM channel numbers.

Pin mappings

The Jetson TX1 has a connector block called the J21 header. However the Python GPIO library needs to reference pins not by their physical pin number, but using a mapping to channel number by either BCM or Broadcom standards.

The physical pin 1 on the TX1 is indicated by a triangle.

Here is a table mapping BCM and Broadcom channel numbers to physical pin numbers. The channel numbers were found in the file /usr/lib/python3/dist-packages/Jetson/GPIO/gpio_pin_data.py.

Physical pin number	Broadcom channel	BCM channel	Sysfs GPIO	Purpose
1				3.3 VDC power
2				5.0 VDC power
3				SDA1
4				5.0 VDC power
5				SCL1
6				GND
7	7	4	gpio216	GPIO_GCLK
8				TXD0
9				GND
10				RXD0
11	11	17	gpio162	GPIO_GEN0
12	12	18	gpio11	GPIO_GEN1
13	13	27	gpio38	GPIO_GEN2
14				GND
15			gpio511	GPIO_GEN3
16	16	23	gpio37	GPIO_GEN4
17				3.3 VDC power
18	18	24	gpio184	GPIO_GEN5
19	19	10	gpio16	SPI_MOSI
20				GND
21	21	9	gpio17	SPI_MISO
22			gpio510	GPIO_GEN6
23	23	11	gpio18	SPI_SCLK
24	24	8	gpio19	SPI_CE0_N
25				GND
26	26	7	gpio20	SPI_CE1_N
27				ID_SDA
28				ID_SCL
29	29	5	gpio219	GPIO5
30				GND
31	31	6	gpio186	GPIO6
32	32	12	gpio36	GPIO12
33	33	13	gpio63	GPIO13
34				GND
35	35	19	gpio8	GPIO19
36	36	16	gpio163	GPIO16
37	37	26	gpio187	GPIO26
38	38	20	gpio9	GPIO20
39				GND
40	40	21	gpio10	GPIO21

Access in Python

We will toggle phyiscal pin 37, which is BCM channel 26 according to the table above.

import Jetson.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(26, GPIO.OUT)
GPIO.output(26, GPIO.HIGH)
print("pin 37 set HIGH")
sleep(10)

GPIO.output(26, GPIO.LOW)
print("pin 37 set LOW")

GPIO.cleanup()
print("i'm done")

This will result in the voltage going to 3.3V for 10 seconds, and then returning to ground. This will be easy to observe with a voltmeter on physical pins 37 and 39, the bottom two pins furthest to the right. Now, that can be linked to a transistor to control an LED or other devices.