GPIO_wtLib.c

#include <stm32f10x.h>
int main(void) {
	int n = 0;
	int button;
	/* Enable the GPIOA (bit 2) and GPIOC (bit 4) */
	/* See 6.3.7 in stm32f100x reference manual */
	RCC ->APB2ENR |= 0x10 | 0x04;
	/* Set GPIOC Pin 8 and Pin 9 to outputs */
	/* 7.2.2 in stm32f100x reference manual */
	GPIOC ->CRH = 0x11;
	/* Set GPIOA Pin 0 to input floating */
	/* 7.2.1 in stm32f100x reference manual */
	GPIOA ->CRL = 0x04;
	while (1) {
		delay ();
// Read the button - the button pulls down PA0 to logic 0
		button = ((GPIOA ->IDR & 0x1) == 0);
		n++;
		/* see 7.2.5 in stm32f100x reference manual */
		if (n & 1) {
			GPIOC ->BSRR = 1 << 8 ;
		} else {
			GPIOC ->BSRR = 1 << 24;
		}
		if ((n & 4) && button) {
			GPIOC ->BSRR = 1 << 9 ;
		} else {
			GPIOC ->BSRR = 1 << 25;
		}
	}
}
void delay(void) {
	int i = 100000; /* About 1/4 second delay */
	while (i-- > 0)
		asm("nop");
}