Man-Machine Interfaces

General Purpose Input Output

An exercise of General Purpose Input Output. Blink LED on target device.

Content

• Requirements
• User Space
• Kernel Space
• Userspace I/O
• Reference

Requirements

• BBG

User Space

SHELL

• Using sysfs interface
  

  echo 49 > /sys/class/gpio/export
  echo out > /sys/class/gpio/gpio49/direction
  
  while :
  do
    echo "Press [CTRL+C] to stop.."
    echo "LED ON  -O-"
    echo 0 > /sys/class/gpio/gpio49/value
    sleep 1
    echo "LED OFF -X-"
    echo 1 > /sys/class/gpio/gpio49/value
    sleep 1
  done
  
  # do this manually if user pressed "Ctrl-C"
  echo 49 > /sys/class/gpio/unexport
  

• PILI

  TBD
  

C

• Using /dev/mem

Python

• Using mraa

Kernel Space

#include <linux/gpio.h>

Userspace I/O

Userspace I/O (UIO)

• Interrupt
• Digital I/O (DIO)

Requirements

• Linux PSP GPIO Driver Guide
• gpio.txt
• BeagleBone Green
• Raspberry Pi 3 Model B+
• MediaTek LinkIt Smart 7688

Reference

http://www.righto.com/2016/08/the-beaglebones-io-pins-inside-software.html https://vadl.github.io/beagleboneblack/2016/07/29/setting-up-bbb-gpio https://vadl.github.io/images/bbb/P8Header.png https://vadl.github.io/images/bbb/P9Header.png

Appendix

GPIO Pin of BBG

• P9 (starting from ETH port)

• P8 (starting from ETH port)

• pingroups

# cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pingroups
registered pin groups:
group: pinmux_uart0_pins
pin 92 (PIN92)
pin 93 (PIN93)