#include "stm32f10x.h"

volatile uint32_t msTicks;

unsigned char InitClk()
{
    unsigned long int TimeOut = 10000;
    //HSE
    RCC->CR   |=  RCC_CR_HSEON;
    while((RCC->CR & RCC_CR_HSERDY)==0)
        if(TimeOut) TimeOut--;
    if(TimeOut==0) return 1;
    RCC->CR   |=  RCC_CR_CSSON;
    RCC->CFGR &= ~RCC_CFGR_SW;
    RCC->CFGR |=  RCC_CFGR_SW_HSE;
    return 0;
}

void USART1_Init(void)
{
    RCC->APB2ENR |=   RCC_APB2ENR_IOPAEN;
    RCC->APB2ENR |=   RCC_APB2ENR_AFIOEN;
    RCC->APB2ENR |=   RCC_APB2ENR_USART1EN;

    GPIOA->CRH   |=   GPIO_CRH_MODE9 | GPIO_CRH_CNF9_1;
    GPIOA->CRH   |=   GPIO_CRH_CNF10_0;
   //Baud rate = F_clk/USART_BRR = 80000000/9600 = 833 = 0x341
    USART1->BRR   =   0x0341;
    USART1->CR1  |=   USART_CR1_UE | USART_CR1_TE | USART_CR1_RE;
}

void USART1_SendData(unsigned char data)
{
    USART1->DR  =  data;
    while((USART1->SR & USART_SR_TC)==0);
    USART1->SR &=  ~USART_SR_TC;
}

unsigned char USART1_ReceiveData(void)
{
    while((USART1->SR & USART_SR_RXNE)==0);
    return   USART1->DR;
}

void Delay (uint32_t dlyTicks)
{
    uint32_t curTicks;

    curTicks = msTicks;
    while ((msTicks - curTicks) < dlyTicks);
}

int main (void)
{
    InitClk();
    USART1_Init();
    SysTick_Config(8000000UL / 1000);    // SysTick 1 msec interrupts
    while (1)
    {
        USART1_SendData('H');
        USART1_SendData('e');
        USART1_SendData('l');
        USART1_SendData('l');
        USART1_SendData('o');
        USART1_SendData('\r');
        Delay(1000);
    }
}

void SysTick_Handler(void)
{
    msTicks++;
}

void NMI_Handler(void)
{
    if (RCC->CIR & RCC_CIR_CSSF) RCC->CIR |= RCC_CIR_CSSC;
}