Add CMSIS bluepill blink.

blue-pill/hello/src/main.cpp

@@ -0,0 +1,31 @@
+#include "stm32f1xx.h"
+#define LEDPORT (GPIOC)
+#define LED1 (13)
+#define ENABLE_GPIO_CLOCK (RCC->APB2ENR |= RCC_APB2ENR_IOPCEN)
+#define _MODER    CRH
+#define GPIOMODER (GPIO_CRH_MODE13_0)
+
+
+void
+ms_delay(int ms)
+{
+   while (ms-- > 0) {
+      volatile int x=500;
+      while (x-- > 0)
+         __asm("nop");
+   }
+}
+
+// Alternates blue and green LEDs quickly
+int
+main(void)
+{
+	ENABLE_GPIO_CLOCK; 		 	// enable the clock to GPIO
+	LEDPORT->_MODER |= GPIOMODER;		// set pins to be general purpose output
+	for (;;) {
+		ms_delay(500);
+		LEDPORT->ODR ^= (1<<LED1); 	// toggle diodes
+	}
+
+	return 0;
+}