#include "stm32f10x.h"

volatile unsigned int TimeTick=0;
volatile unsigned int oneMsTick=0;

void TIM3_IRQHandler(void)
	{
	//debugging: one high-pulse on GPIO A3
	GPIOA->BSRR = GPIO_Pin_3;
	GPIOA->BRR  = GPIO_Pin_3;

	TimeTick++;
	oneMsTick++;

	TIM3->SR = (uint16_t)~TIM_IT_Update;

	//statement with no effect (but on volatile variable , so it cannot be optimized out completely)
	//does not change target size, but changes behaviour for optimization O3 (not for O0)  --> gcc optimization bug??
	TimeTick;
	}

int main(void)
	{
	//Sysinit at 48MHz,   optimization: O3

	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);

	// GPIOA Periph clock enable
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

	GPIO_InitTypeDef GPIO_InitStructure;
	// Configure PA3 in output pushpull mode
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
	GPIO_Init(GPIOA, &GPIO_InitStructure);

	//timer init
	TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
	RCC_ClocksTypeDef RCC_ClocksStatus;
	NVIC_InitTypeDef NVIC_InitStructure;

	/* Enable timer clocks */
	RCC_APB1PeriphClockCmd( RCC_APB1Periph_TIM3, ENABLE );

	TIM_TimeBaseStructInit( &TIM_TimeBaseStructure );

	/* Value clock source */
	RCC_GetClocksFreq(&RCC_ClocksStatus);

	/* Initialize register */
	TIM_DeInit( TIM3 );

	/* Enable the TIM3 global Interrupt */
	NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
	NVIC_Init(&NVIC_InitStructure);

	/* Time base configuration for timer  - which generates the interrupts. */
	TIM_TimeBaseStructure.TIM_Period = 1918;
	TIM_TimeBaseStructure.TIM_Prescaler = (RCC_ClocksStatus.PCLK1_Frequency  / 1000000);
	TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
	TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
	TIM_TimeBaseInit( TIM3, &TIM_TimeBaseStructure );

	TIM_ARRPreloadConfig( TIM3, ENABLE );
	TIM_ITConfig( TIM3, TIM_IT_Update, ENABLE );

	/* Finally, enable timer... */
	TIM_Cmd( TIM3, ENABLE );


	while (1)
		{//wait forever - do nothing
		}

	}