Simple Python software to control GPIO

In this part of the lab you will add GPIO ports to your hardware, then you will use it in bash shell and finally in Python3 software.

Add GPIO hardware

In Vivado add the hardware blocks AXI GPIO (in block diagram) to your system and connect them to LEDs and buttons on Zybo board. Note the addresses on AXI bus of the added GPIOs. This will be needed later to identify the GPIO ports in Linux.

Add required layer and software (Python gpiod)

To use the GPIOs in Python, you will need gpiod package for Python.

Login to your Yocto build system on workstation:

1. Add new layer needed for this package: meta-openembedded/meta-python:

bitbake-layers add-layer ../meta-openembedded/meta-python

2. Build rpm:

bitbake python3-gpiod

First test of GPIOs

Continue on Zybo board.

1. Install new RPM on Zybo Linux board

2. Identify the GPIO ports on the board:

• Check in sys:

ls /sys/class/gpio/<gpioXXX>/label

• Look at device tree, then see which GPIO chips are available in your system:

tree /sys/class/gpio
/sys/class/gpio
|-- export
|-- gpiochip1016 -> ../../devices/soc0/amba_pl/41210000.gpio/gpio/gpiochip1016
|-- gpiochip1020 -> ../../devices/soc0/amba_pl/41200000.gpio/gpio/gpiochip1020
|-- gpiochip898 -> ../../devices/soc0/axi/e000a000.gpio/gpio/gpiochip898
`-- unexport

Each gpiochipN represents a GPIO controller.

• For each chip read base and number  of pins.

cat /sys/class/gpio/gpiochip1020/base
cat /sys/class/gpio/gpiochip1020/ngpio

For example for:

base = 1020
ngpio = 4

that means that we can use GPIOs: 1020, 1021, 1022, 1023.

3. Export single pin for LED0 … LED3:

echo 1020 > /sys/class/gpio/export 2>/dev/null
echo 1021 > /sys/class/gpio/export 2>/dev/null
echo 1022 > /sys/class/gpio/export 2>/dev/null
echo 1023 > /sys/class/gpio/export 2>/dev/null

4. Now you can use the names: gpio1020, gpio1021, gpio1022, gpio1023. Set each pin's direction as output:

echo out > /sys/class/gpio/gpio1020/direction
echo out > /sys/class/gpio/gpio1021/direction
echo out > /sys/class/gpio/gpio1022/direction
echo out > /sys/class/gpio/gpio1023/direction

5. Turn on  LEDs:

echo "1" > /sys/class/gpio/gpio1020/value
echo "1" > /sys/class/gpio/gpio1021/value
echo "1" > /sys/class/gpio/gpio1022/value
echo "1" > /sys/class/gpio/gpio1023/value

6. To turn off LEDs:

echo "0" /sys/class/gpio/gpio1020/value
echo "0" /sys/class/gpio/gpio1021/value
echo "0" /sys/class/gpio/gpio1022/value
echo "0" /sys/class/gpio/gpio1023/value

7. Similarly, check the switches. i.e for SW0:

echo 1016 > /sys/class/gpio/export 2>/dev/null
echo in > /sys/class/gpio/gpio1016/direction
cat /sys/class/gpio/gpio1016/value

Unexport all used GPIO pins before you start using GPIOs in Python:

echo 1020 > /sys/class/gpio/unexport
echo 1021 > /sys/class/gpio/unexport
echo 1022 > /sys/class/gpio/unexport
echo 1023 > /sys/class/gpio/unexport
echo 1016 > /sys/class/gpio/unexport

Python3 software to mirror buttons to LEDs

Write a Python3 script to continuously read all 4 switches and reflect their state on 4 LEDs. Use the commands from gpiod package. Here are some hints regarding the commands that can be used:

import gpiod
gpiod.Chip(dev)
gpiod.LineSettings()
gpiod.line.Direction
gpiod.line.Value
gpiod.line.Value.INACTIVE)