SAKS hat for raspberry_pi

SAKS = Swiss Army Knife Shield for Raspberry Pi

How other library control GPIO

wiringpi system but uses the /sys/class/gpio interface rather than accessing the hardware directly(softPwmWrite)

sprintf(fName, "/sys/class/gpio/gpio%d/value", i)

1. /sys/class/gpio: sysfs_gpio(deprecated), gpio(deprecated), maybe not working in pi4B
2. /dev/gpiomem or /dev/gpiochip0: rppal, wiringpi, gpio-cdev
3. /dev/pigpio and pigpio daemon process: pigpio

Some questions need to solve

• Why gpio access from /dev/gpiomem via mmap syscall is faster than format!("/sys/class/gpio/gpio{}/active_low", gpio_num)
• Why gpio pin number has three encoding?(BOARD, BCM, wiringpi)
• About the onboard_led(/sys/class/leds/led0/) like arduino's LED_BUILTIN

My raspberry_pi notes

CPU temperature

vcgencmd measure_temp

Setup raspberry_pi

How to connect raspberry_pi without internet/display/GUI Desktop?

1. put empty ssh file to SD card root directory in order to enable SSH on first time boot
2. SSH to pi via ethernet cable or serial(RS-232 with RXD+TXD+GND, don't connect 5V pin!) port