ATTNode v3 Firmware Now Uses PlatformIO

Recently PlatformIO added support for the Microchip ATTiny3216 used on the ATTNode v3. Starting today, all further development of the official firmware will use PlatformIO as the coding environment instead of Arduino IDE, because of the far better IDE, sensible library management and automated project configuration.

The old Arduino IDE variant of the firmware is archived as a separate branch arduinoide in the Git repository for reference purposes, but any new development will use the PlatformIO variant.