STM32L452 serial example

Developed with Rust Cortex M support library, this code implements the UART interface on the STM32L452 chip. Tested with the Nucleo STM32L452RE-P

Screen /dev/ttyACM0 at 115200 baud rate, see "Hello, world!" appear.

It also blinks the LED using a timer, because of course there should be a blinkenlicht!

Build using cargo build --release --target thumbv7em-none-eabihf using a Nightly rust, works with 2018-09-20.

Notes & tips

The Nucleo -p version with SMPS does not have an external HSE crystal. This would not be worth knowing if the default clock source weren't the MSE clock, which is inaccurate, and thus not suitable for driving the USART clock. Example using the MSI clock, with auto-calibration.
The write() function in the peripherals lib operates on an internal reset state, not he current value in the target register. Use modify() if you want to base the modification on the current register state
If something does not work as expected, but also does not trigger any faults, it's the clock source. It's always the clock source. Use MXCube for figuring out the clock configuration values.
The svd command provided by the gdb.py script (check inside for install instructions) is a lifesafer.
Use Atollic TrueStudio when in need of a decent GDB GUI

cleanup