Assignment of peripherals and pins
==================================

SPI2	emulated TM1618 LED driver
USART1	debugging


			   Blue Pill pinout
			+--------------------+
			| VBATT		3.3V |
BluePill LED		| PC13		 GND |
			| PC14		  5V |
			| PC15		 PB9 |
			| PA0		 PB8 |
			| PA1		 PB7 |
			| PA2		 PB6 |
			| PA3		 PB5 |
			| PA4		 PB4 |
			| PA5		 PB3 |
			| PA6		PA15 |
			| PA7		PA12 |
			| PB0		PA11 |
			| PB1		PA10 |  RXD1 - debugging console
			| PB10		 PA9 |  TXD1 - debugging console
			| PB11		 PA8 |
			| RESET		PB15 |	MOSI2 - LED driver data input
			| 3.3 V		PB14 |	MISO2 - unused
			| GND		PB13 |	SCK2 - LED driver clock
			| GND		PB12 |	SS2 - unused
			+--------------------+