Python UPDI driver for programming "new" tinyAVR and megaAVR devices

pyupdi is a Python utility for programming AVR devices with UPDI interface using a standard TTL serial port.

Connect RX and TX together with a suitable resistor and connect this node to the UPDI pin of the AVR device.

Be sure to connect a common ground, and use a TTL serial adapter running at the same voltage as the AVR device.

                        Vcc                     Vcc
                        +-+                     +-+
                         |                       |
 +---------------------+ |                       | +--------------------+
 | Serial port         +-+                       +-+  AVR device        |
 |                     |      +----------+         |                    |
 |                  TX +------+   4k7    +---------+ UPDI               |
 |                     |      +----------+    |    |                    |
 |                     |                      |    |                    |
 |                  RX +----------------------+    |                    |
 |                     |                           |                    |
 |                     +--+                     +--+                    |
 +---------------------+  |                     |  +--------------------+
                         +-+                   +-+
                         GND                   GND

When running pyupdi on Raspberry pi, use GPIOs 14 and 15 for UART TX and RX. On rpi3, be sure to apply the device tree overlay to map UART0/ttyAMA0 to these pins (relocate or disable Bluetooth device). More information here: https://www.raspberrypi.org/documentation/configuration/uart.md