STM32F103 SPI1->DR显示为0x00

澜月亮提问时间：2015-6-16 11:34 /

GPIO_InitTypeDef GPIOB_InitStructure;
SPI_InitTypeDef SPI_InitStructure;
void RCC_Configuration(void)
{
      RCC_DeInit();
      SystemInit();
      RCC_APB2PeriphClockCmd( RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA
                        |RCC_APB2Periph_GPIOB | RCC_APB2Periph_GPIOC  | RCC_APB2Periph_AFIO
                                                , ENABLE);
      RCC_APB2PeriphClockCmd( RCC_APB2Periph_SPI1 , ENABLE);
}
void GPIO_Configuration(void)
{

      GPIO_PinRemapConfig(GPIO_Remap_SWJ_JTAGDisable,ENABLE);
      GPIO_PinRemapConfig(GPIO_Remap_SPI1,ENABLE);
      //SCK-PB3,MOSI-PB5
      GPIOB_InitStructure.GPIO_Pin = GPIO_Pin_3|GPIO_Pin_5;
      GPIOB_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
      GPIOB_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
      GPIO_Init(GPIOB,&GPIOB_InitStructure);

      //MISO-PB4
      GPIOB_InitStructure.GPIO_Pin = GPIO_Pin_4;
      GPIOB_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
      GPIO_Init(GPIOB,&GPIOB_InitStructure);
}
      u8 SPI1_ReadWriteByte(u8 TxData)
{
SPI1->DR = TxData;
while (!(SPI1->SR & 0x01));
   return (SPI1->DR);
}

      void SPI_Configuration(void)
{

      SPI_Cmd(SPI1, DISABLE);
  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_128;//56M/128=437.5K
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
  SPI_Init(SPI1, &SPI_InitStructure);

  SPI_Cmd(SPI1, ENABLE);
      SPI1_ReadWriteByte(0xff);
}
在SPI1_ReadWriteByte(0xff);处设置断点，单步运行，发现SPI1->DR 寄存器数据一直显示为0x00.请各位技术大牛帮忙看看