When STM32F4 based flight controllers made its way to the world of MultiWii derivatives (Cleanflight and whole family), all I think all developers assumed that SoftwareSerial feature will not be needed on those boards. Why it should be? STM32F4 has enough hardware UARTs to satisfy everyones needs.
Unfortunately, live had it's own point of view on that topic:
- Most F4 flight controllers have only 2 to 3 hardware UARTs available and usually one of them is shared with I2C (Revolution, Airbot F4)
- STM32F4 does not have internal hardware inverters. Hardware manufacturers usually put only one external inverter for S.Bus and that's all
Because of that, Software Serial feature is coming back to F4 boards. Together with INAV 1.5, SoftSerial will be available on Airbot F4 / Flip32 F4 target on two small pads located near UART3 connector. RX line on pad CH5, TX line on CH6 line. Pads are quite small, but with basic soldering skills and decent soldering iron there should be no problems to solder thin cables to them.
Since F4 CPU is much more powerful than F1, limitation of 19200bps on Software Serial UARTs is no longer actual. I have tested 57600bps and 115200bps should be archivable.