Add STM32 Examples

[jhugon]

Probably want to use STM32F091 first

Use libopencm3. Maybe difficult to integrate with build system. Could start with libopencm3 as a git sub repo?

• [ ] Add STM32 Integration Tests like Arduino
  • [x] "asc_loopback"
  • [x] "adc_streaming" with register pointer to LED (so a test on the way to the other)
• [x] Add STM32 Blink
• [x] Add STM32 UART Test

https://github.com/libopencm3/libopencm3 https://github.com/libopencm3/libopencm3-examples

[jhugon]

Maybe these make files can help https://github.com/libopencm3/libopencm3/tree/master/mk

[jhugon]

Instead, maybe could use linker script from opencm3 with driver lib from https://github.com/STMicroelectronics/STM32Cube_MCU_Overall_Offer

It looks like an assembler script that sets up the interrupts from the ST examples would be useful too

[jhugon]

ST provides linker and assembler startup script here: https://github.com/STMicroelectronics/STM32CubeF0/tree/master/Projects/STM32F091RC-Nucleo/Templates/SW4STM32

not sure how easy that will be to get working

[jhugon]

Having trouble with UART loopback, and the board makes it difficult to check with a scope/logic-analyzer b/c the UART isn't connected to any pins. You have to solder a jumper!

[jhugon]

Atomic ops: https://libopencm3.org/docs/latest/stm32l1/html/group__CM3__cortex__atomic__defines.html

[jhugon]

Usart interrupt example: https://github.com/libopencm3/libopencm3-examples/blob/master/examples/stm32/f4/stm32f429i-discovery/usart_irq/usart_irq.c