opencm3-ex/serplus

This is STM32F072 port of jcw's SerPlus:

• https://github.com/jeelabs/embello/tree/master/explore/1649-f103/serplus
• https://jeelabs.org/article/1649f/
• https://github.com/jeelabs/folie

Modifications

• runs on F072, aimed for the bat board, with [SerPlus shield], which has some extra features, so:
• button controlled mode: either "SerPlus mode" or straight "raw UART with DTR"
• WS2812 neopixel status LED
• control on/off output power with a FET
• measure output power level using ADC
• these can be turned off via #defines in the code

In "raw" mode, it works as any other USB-to-serial converter (with DTR), so it can be used to upload firmware to arduino-type boards (tested).

Original Serplus README

SerPlus is an STM32F103-based bridge between USB and a serial port.

Inline telnet escape codes can be used to control DTR, RTS, and parity.

Based on the usart1_irq_printf and usb_cdcacm code from libopencm3-examples (LGPL3).

For the RAM-based version, to be loaded at $20002000, use:

make -f Makefile-ram