void USART1_IRQHandler(void)
{
    //Receive Data register not empty interrupt
      if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
   {
       rx=1;
       USART_ClearITPendingBit(USART1, USART_IT_RXNE);
       tmp=USART_ReceiveData (USART1);

   }
      //Transmission complete interrupt
      if(USART_GetITStatus(USART1, USART_IT_TC) != RESET)
      {
          USART_ClearITPendingBit(USART1, USART_IT_TC);
          tx_end=1;
      }

#define USART1_BUF_SIZE (64)
#define USART1_BUF_MASK (USART1_BUF_SIZE - 1)

typedef struct {
uint8_t buf [USART1_BUF_SIZE];
uint8_t in;
uint8_t out;
uint8_t count;
} usart1_buf_t;

volatile static usart1_buf_t usart1_rx, usart1_tx;

extern void usart1_putchar (uint8_t symb) {
if ((USART1->SR & USART_SR_TXE) && !usart1_tx.count) {
USART1->DR = symb;
} else if (usart1_tx.count < USART1_BUF_SIZE) {
usart1_tx.buf [usart1_tx.in++] = symb;
usart1_tx.count++;
usart1_tx.in &= USART1_BUF_MASK;
};
};

extern uint8_t usart1_getchar (void) {
uint8_t symb;
if (usart1_rx.count > 0) {
symb = usart1_rx.buf [usart1_rx.out++];
usart1_rx.count--;
usart1_rx.out &= USART1_BUF_MASK;
return symb;
};
return 0;
};

void USART1_IRQHandler (void) {
if (USART1->SR & USART_SR_TC) {
USART1->SR &= ~USART_SR_TC;
if (usart1_tx.count > 0) {
USART1->DR = usart1_tx.buf [usart1_tx.out++];
usart1_tx.count--;
usart1_tx.out &= USART1_BUF_MASK;
};
} else if (USART1->SR & USART_SR_RXNE) {
USART1->SR &= ~USART_SR_RXNE;
if (usart1_rx.count < USART1_BUF_SIZE) {
usart1_rx.buf [usart1_rx.in++] = USART1->DR;
usart1_rx.in &= USART1_BUF_MASK;
usart1_rx.count++;
};
};
};