raspberry pi 5 sysfs + udev to control gpio

trigger.sh

#!/bin/bash

if [ $1 == 'CH1' ] ;	then # gpio 26, PIN37
 ch=425
elif [ $1 == 'CH2' ] ;	then # gpio 20, PIN38
 ch=419
elif [ $1 == 'CH3' ]; 	then # gpio 21, PIN40
 ch=420
else
 echo "Parameter error"
 exit
fi

	echo $ch  > /sys/class/gpio/export

	flag=true
	while $flag ; do
		# ls -l /sys/class/gpio/gpio$ch/
		echo waiting for udev to set permission right
		echo out > /sys/class/gpio/gpio$ch/direction
		if [ $? -eq 0 ] ; then
			flag=false
		else
			flag=true
		fi
		sleep 1
	done

	echo 0 > /sys/class/gpio/gpio$ch/value
	sleep 1
	echo 1  > /sys/class/gpio/gpio$ch/value

	echo $ch  > /sys/class/gpio/unexport

exit

# https://www.kernel.org/doc/Documentation/gpio/sysfs.txt
# https://stackoverflow.com/questions/76138933/raspberry-pi-gpio-sysfs-fopen-permission-denied
# https://doc.embedfire.com/linux/imx6/linux_base/zh/latest/linux_app/gpio_subsystem/gpio_subsystem.html

# grep PIN /sys/kernel/debug/gpio