void startup(void) __attribute__((naked)) __attribute__((section (".start_section")) );

void startup ( void )
{
__asm volatile(
	" LDR R0,=0x2001C000\n"		/* set stack */
	" MOV SP,R0\n"
	" BL main\n"				/* call main */
	"_exit: B .\n"				/* never return */
	) ;
}

#define GPIO_E 0x40021000
#define GPIO_E_MODER 		((volatile unsigned int   *) 	(GPIO_E))

#define GPIO_D	0x40020C00
#define GPIO_D_MODER 		((volatile unsigned int *) 		(GPIO_D))
#define GPIO_D_OTYPER    	((volatile unsigned short *) 	(GPIO_D + 0x04))
#define GPIO_D_PUPDR    	((volatile unsigned int   *)   	(GPIO_D + 0xC ))

#define GPIO_D_IDR_HIGH 	((volatile unsigned char  *)  	(GPIO_D + 0x11))
#define GPIO_D_ODR_HIGH    	((volatile unsigned char  *)  	(GPIO_D + 0x15))
#define GPIO_D_ODR_LOW 		((volatile unsigned char *) 	(GPIO_D + 0x14))

#define SYSCFG_EXTICR1	0x40013808
#define EXTI_RTSR		0x40013C0C
#define EXTI_IMR		0x40013C00
#define EXTI_PR				((volatile unsigned int *) 		(0x40013C14))

static volatile unsigned int count = 0;

void interrupt_handler(void) {
	if((*((unsigned int *) 0x40013C14) & 0x8) != 0) {
		count++;
		*((unsigned int *) 0x40013C14) |= 0x8;
	}
}

void init_app(void) {
	*GPIO_D_MODER &= 0xFFFF0000;
	*GPIO_D_MODER |= 0x00005555;

	*((unsigned int *) 0x40013808) &= ~0xF000;
	*((unsigned int *) 0x40013808) |=  0x4000;


	*((unsigned int *) 0x40013C00)  |=  8;
	*((unsigned int *) 0x40013C0C)  |=  8;
	*((unsigned int *) 0x40013C08)  &= ~8;

	*((void (**) (void) ) 0x2001C064 ) = interrupt_handler;

	*((unsigned int *) 0xE000E100) |= (1<<9);
}

void main(void) {
	init_app();
	while(1) {
		*GPIO_D_ODR_LOW = count;
	}
}