NOTES

Raspberry Pi (Zero 2W) related stuffs

Zero 2W has 2 micro USB ports. One for power only, and another for USB dual-role port.

1. Serial debug

/boot/firmware/config.txt:

[all]
enable_uart=1

2. Scriptable keyboard, mouse, and screen

make_keyboard.sh works on Raspberry Pi Zero 2W, as well. But, you have to set the microUSB port as “otg” or “peripherial” mode in /boot/firmware/config.txt.

[all]
dtoverlay=dwc2

3. GPIO

GPIO pins can be accessed by

1. /sys/class/gpio

   cd /sys/class/gpio
       echo $((512+26)) > export
       cd gpio538
           echo out > direction
           echo 1 > value
           echo 0 > value
   

   and to reset the pin,

   cd /sys/class/gpio
       echo 538 > unexport
   

2. gpioget, gpioset

   gpioget -c0 26
   gpioset -c0 26=on
   gpioset -c0 26=off
   

4. PWM (Pulse Width Modulaton)

Zero 2W has 2 PWM channels:

pwm	pin	gpio	func	mode
PWM0	PIN32	GPIO12	4	Alt0
PWM1	PIN33	GPIO13	4	Alt0

There are many ways to produce PWM from Zero 2W.

1. GPIO PWM — Use -t option of gpioset:
   • gpioset -t1,1 -c0 26=on — turn on 1ms, turn off 1ms, and repeat. About 500Hz with 50% duty cycle, but not accurate.
2. Software PWM — Any GPIO pin can be used as “software PWM”. It needs “device tree” modules in /boot/firmware/config.txt:
   • dtoverlay=pwm-gpio,gpio=16 — Accessing software PWM is the same as hardware PWM.

     cd /sys/class/pwm/pwmchip0
         echo 0 > export      # --> pwm0
         cd pwm0
             echo $((2*1000*1000)) > period          # 2ms = 500Hz
             echo $((1*1000*1000)) > duty_cycle      # 1ms = 50%
             echo 1 > enable
     

3. Hardware PWM (single channel) — One of PWM0 or PWM1, but not both. It needs “device tree” modules in /boot/firmware/config.txt:
   • dtoverlay=pwm,pin=12,func=4 — will enable only PWM0.

     echo 0 > /sys/class/pwm/pwmchip0/export    # --> pwm0
     

   • dtoverlay=pwm,pin=13,func=4 — will enable only PWM1.

     echo 1 > /sys/class/pwm/pwmchip0/export    # --> pwm1
     

4. Hardware PWM (dual channel) — Both PWM0 and PWM1 can be used.
   • dtoverlay=pwm-2chan,pin=12,func=4,pin2=13,func2=4

     echo 0 > /sys/class/pwm/pwmchip0/export    # --> pwm0
     echo 1 > /sys/class/pwm/pwmchip0/export    # --> pwm1
     

5. After using the pins as “input”, to revert the pin back to PWM pins,

   pinctrl set 12,13 a0    # --> a0 = Alt0