Beaglebone Black GPIO - 8x8 LED Matrix with C Program - Part3

STEP-4 : Setting up the Start-up Script and make active at boot-up

• In order to work with device tree overlay what we have created in previous step, we need to write a start-up script.
• The C code we are going to use is have some issues with GPIO ports like "Bus Error" when the compiled file is executed.
• Based on this website the issue got resolved when we export one pin on each GPIO port. So this we need to add it on start-up script.
• This start-up script will be executed every time the Beaglebone Black is started.
•  Make a start-up script with the following steps:

       root@beaglebone:# vi /usr/bin/init_boot.sh
   
        Copy and Pase following lines in "init_boot.sh" file - Download

 #!/bin/bash
echo 5 > /sys/class/gpio/export

echo 33 > /sys/class/gpio/export

echo 65 > /sys/class/gpio/export

echo 115 > /sys/class/gpio/export

export SLOTS=/sys/devices/bone_capemgr.8/slots

echo GPIO-Test > $SLOTS

• To save and exit the file press "Esc" type ":wq" and Enter.
• Now start-up script is ready to make active at booting process.
• To make start-up script active at booting process, make a service with the following lines:

      root@beaglebone:# vi /lib/systemd/init_boot.service

[Unit]
Description=Enable GPIO Pins
After=syslog.target network.target

[Service]
Type=simple
ExecStart=/usr/bin/init_boot.sh

[Install]
WantedBy=multi-user.target

• To save and exit the file press "Esc" type ":wq" and Enter.
• Make a symbolic link

    root@beaglebone:# cd /etc/systemd/system/
    root@beaglebone:# ln /lib/systemd/init_boot.service init_boot.service

• Make systemd take notice of it, activate the service immediately and enable the service to be started on boot-up

   root@beaglebone:# systemctl daemon-reload
   root@beaglebone:# systemctl start init_boot.service   
   root@beaglebone:# systemctl enable init_boot.service

• Now the start-up script is active.
• To check whether start-up script is active restart the beaglebone black.
• Run following commands:

    To check GPIO pins 5, 33, 65 & 115 are exported:

   root@beaglebone:# ls -al /sys/class/gpio

root@beaglebone:# ls -al /sys/class/gpio/total 0
drwxr-xr-x  2 root root    0 Jan  1 05:00 .
drwxr-xr-x 48 root root    0 Jan  1 05:00 ..
--w-------  1 root root 4096 Jan  1 05:00 export
lrwxrwxrwx  1 root root    0 Jan  1 11:30 gpio115 -> ../../devices/virtual/gpio/gpio115
lrwxrwxrwx  1 root root    0 Jan  1 11:30 gpio33 -> ../../devices/virtual/gpio/gpio33
lrwxrwxrwx  1 root root    0 Jan  1 11:30 gpio5 -> ../../devices/virtual/gpio/gpio5
lrwxrwxrwx  1 root root    0 Jan  1 11:30 gpio65 -> ../../devices/virtual/gpio/gpio65lrwxrwxrwx  1 root root    0 Jan  1 05:00 gpiochip0 -> ../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx  1 root root    0 Jan  1 05:00 gpiochip32 -> ../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx  1 root root    0 Jan  1 05:00 gpiochip64 -> ../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx  1 root root    0 Jan  1 05:00 gpiochip96 -> ../../devices/virtual/gpio/gpiochip96
--w-------  1 root root 4096 Jan  1 05:00 unexport

   To check the device tree overlay is loaded:
   root@beaglebone:# cat /sys/devices/bone_capemgr.8/slots

 root@beaglebone:/lib/firmware# cat $SLOTS
 0: 54:PF---
 1: 55:PF---
 2: 56:PF---
 3: 57:PF---
 4: ff:P-O-- Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
 5: ff:P-O-- Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
 6: ff:P-O-- Bone-Black-HDMIN,00A0,Texas Instrument,BB-BONELT-HDMIN
 7: ff:P-O-L Override Board Name,00A0,Override Manuf,GPIO-Test

• It is loaded on 7th slot. 

STEP-5 : Proceed for C code

• Download C Coded from Here