#include <stdint.h>

#include "reg.h"

/* USART TXE Flag

* This flag is cleared when data is written to USARTx_DR and

* set when that data is transferred to the TDR

*/

#define USART_FLAG_TXE ((uint16_t) 0x0080)

void print_str(const char *str)

{

while (*str) {

while (!(*(USART2_SR) & USART_FLAG_TXE));

*(USART2_DR) = (*str & 0xFF);

str++;

}

}

void main(void)

{

*(RCC_APB2ENR) |= (uint32_t) (0x00000001 | 0x00000004);

*(RCC_APB1ENR) |= (uint32_t) (0x00020000);

/* USART2 Configuration, Rx->PA3, Tx->PA2 */

*(GPIOA_CRL) = 0x00004B00;

*(GPIOA_CRH) = 0x44444444;

*(GPIOA_ODR) = 0x00000000;

*(GPIOA_BSRR) = 0x00000000;

*(GPIOA_BRR) = 0x00000000;

*(USART2_CR1) = 0x0000000C;

*(USART2_CR2) = 0x00000000;

*(USART2_CR3) = 0x00000000;

*(USART2_CR1) |= 0x2000;

print_str("Hello World!\n");

while (1);

}