USART_send("I am iron man, I am iron man, I am iron man, I am iron man, I am iron man, I am iron man\r\n");
         USART_send("AT\r\0");
         put_string("AT sent\r\n");
         while (!kbdread()) {
            if (IsRxdata()) put_char(USART_receive());
         }

#include <stm32f0xx.h>
#define USART   USART1
#define FIFO_BUFFER_SIZE   160

void USART_Init(void) {
   RCC->APB2ENR |= RCC_APB2ENR_USART1EN;
   
   USART->CR1 = USART_CR1_RXNEIE;
//   USART->CR3 = USART_CR3_CTSE | USART_CR3_RTSE;
   USART->BRR = 0x1388; // 9600: oversample 16, Fck=48MHz
   
   USART->CR1 |= USART_CR1_TE | USART_CR1_RE | USART_CR1_UE;
   NVIC_EnableIRQ(USART1_IRQn);
}

unsigned char    RxFIFObuf[FIFO_BUFFER_SIZE],
   *Rx_rd_ptr =  RxFIFObuf,
   *Rx_wr_ptr =    RxFIFObuf;

void USART1_IRQHandler(void) {
   if (USART->ISR & USART_ISR_RXNE) {
      unsigned char * old_rx_ptr;
      old_rx_ptr = Rx_wr_ptr;
      *Rx_wr_ptr++ = USART->RDR;
      if (Rx_wr_ptr > &RxFIFObuf[FIFO_BUFFER_SIZE - 1]) {
         Rx_wr_ptr = RxFIFObuf;
      }
      if (Rx_wr_ptr == Rx_rd_ptr) {
         Rx_wr_ptr = old_rx_ptr; // overflow!
      }
   }
   if (USART->ISR & USART_ISR_TXE) {
   }
}

unsigned int IsRxdata(void) {
   return (Rx_rd_ptr == Rx_wr_ptr) ? 0 : 1;
}

unsigned char USART_receive(void) {
   unsigned char result;
   while (Rx_rd_ptr == Rx_wr_ptr) continue;
   result = *Rx_rd_ptr++;
   if (Rx_rd_ptr > &RxFIFObuf[FIFO_BUFFER_SIZE - 1]) {
      Rx_rd_ptr = RxFIFObuf;
   }
   return result;
}

void USART_send(char * string) {
   while (*string) {
      while (!(USART->ISR & USART_ISR_TXE)) continue;
      USART->TDR = *string++;
   }
}