4.1 GPIO Test

This example demonstrates how to use Linux API to control GPIO of MYD-C437X-PRU development board, please refer to the source code for detail.

Hardware Preparation：

• One MYD-C437X-PRU development board
• One USB to TTL converter used to connect J25 of MYD-C437X-PRU development board and host PC, set the baudrate of serial port on host PC to 115200-8-n-1

Software Preparation:

• Linux Kernel 4.1.18
• gpio_test application

Test Steps:

• Copy cross compiled <WORKDIR>/Examples/gpio/gpio_test to /usr/bin directory of the MYD-C437X-PRU development board, run gpio_test application as below:

# gpio_test -h
Usage: gpio_test [options]

Version 1.0
Options:
-n | -- number gpio    gpio number.
-g | -- get            get gpio level.
-s | -- set  level     set gpio level. 0: low; 1: high
-h | -- help            Print this message

• GPIO3_7 is used as the write-protect pin, write-protect is enabled when GPIO3_7 outputs high, disabled when GPIO3_7 outputs low.
  Test with gpio_test application as below:

# gpio_test -n 103 -s 1
==gpio3_7  direction is out
==gpio3_7  level is high
Set gpio3_7 level high success!
# gpio_test -n 103 -s 0
==gpio3_7  direction is out
==gpio3_7  level is low
Set gpio3_7 level low success!

Users can also control GPIO by executing echo and cat commands to write and read /sys/class/gpio in a shell script, For example, there is a bash script named as /usr/bin/set_eeprom.sh used for controlling GPIO3_7, the content of file is shown below:

#!/bin/bash

EEPROM_WP_GPIO_PIN=103

wait_gpio() {
        sleep 1
}

wp_init() {
        if [ ! -d "/sys/class/gpio/gpio$EEPROM_WP_GPIO_PIN" ]; then
                echo "$EEPROM_WP_GPIO_PIN" > /sys/class/gpio/export; wait_gpio
        fi

        echo "out" > /sys/class/gpio/gpio$EEPROM_WP_GPIO_PIN/direction; wait_gpio
}

up() {
        echo "0" > /sys/class/gpio/gpio$EEPROM_WP_GPIO_PIN/value; wait_gpio
}

down() {
        echo "1" > /sys/class/gpio/gpio$EEPROM_WP_GPIO_PIN/value; wait_gpio
}

if [ "$1" = "1" ]; then
        wp_init
        up
fi

if [ "$1" = "0" ]; then
        wp_init
        down
        echo "$EEPROM_WP_GPIO_PIN" > /sys/class/gpio/unexport; wait_gpio
fi

• Run /usr/bin/set_eeprom.sh to control the write-protect pin of EEPROM：

# chmod 777 /usr/bin/set_eeprom.sh
# set_eeprom.sh 1                            -- Enable write-protect
# set_eeprom.sh 0                            -- Disable write-protect