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Raspberry Pi

These notes are based on an install of the 32-bit Raspberry Pi OS Lite.

Development Libraries and Tools

sudo apt -y install pigpio-tools

Check I2C Clock Speed

#!/bin/sh
# Print current maximum i2c rate
var="$(xxd /sys/class/i2c-adapter/i2c-1/of_node/clock-frequency | awk -F': ' '{print $2}')"
var=${var//[[:blank:].\}]/}
printf "I2C Clock Rate: %d Hz\n" 0x$var

Hardware PWM

All Raspberry Pi models have at least one hardware PWM channel as per the table below.

GPIO PWM Channel Func Models
12 0 4 All except the original model A and B
13 1 4 All except the original model A and B
18 0 2 All
19 1 2 All except the original model A and B
40 0 4 CM1-3 only
41 1 4 CM1-3 only
45 1 4 CM1-3 only
52 0 5 CM1-3 only
53 1 5 CM1-3 only

These values were taken from the file /boot/overlays/README.

By default, configuring the hardware PWM channel is only possible via relatively complex memory-mapped register configuration which require root access to modify. Fortunately pigpio can handle all of this complexity for us - full hardware PWM control is available via the pigpioj provider.

Hardware PWM control is also possible via the Linux sysfs interface. To enable one hardware PWM channel add dtoverlay=pwm to /boot/config.txt (using the GPIO and Func values in the table above) and reboot. For example, to enable hardware PWM channel 0 on GPIO 12:

dtoverlay=pwm,pin=12,func=4

After a reboot the sysfs directory /sys/class/pwm/pwmchip0/pwm0 should be present.

Alternatively, two hardware PWM channels can be configured by adding dtoverlay=pwm-2chan to /boot/config.txt. For example, to enable hardware PWM channel 0 on GPIO 18 and channel 1 on 19:

dtoverlay=pwm-2chan,pin=18,func=2,pin2=19,func2=2

Make sure you add only one of the above and verify that the settings are correct before rebooting.

ARMv6 - Original Pi Zero, Pi Models A/B

diozero now requires JDK-11 as a minimum, however, the OpenJDK 11 and later versions in raspbian do not run on ARMv6. Fortunately the Azul OpenJDK 11 version does support ARMv6.

Download the latest version of Azul OpenJDK 11 for ARMv6/7 from the Azul downloads page.

At the time of writing, this was build 11.60.19-ca:

cd
wget https://cdn.azul.com/zulu-embedded/bin/zulu11.60.19-ca-jdk11.0.17-linux_aarch32hf.tar.gz
cd /usr/lib/jvm
sudo tar xf ~/zulu11.60.19-ca-jdk11.0.17-linux_aarch32hf.tar.gz
sudo ln -s zulu11.60.19-ca-jdk11.0.17-linux_aarch32hf java-11-zulu-armhf
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-11-zulu-armhf/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-11-zulu-armhf/bin/javac 1
sudo update-alternatives --config java
sudo update-alternatives --config javac