Electronic – STM32 SPI Slave send data Problem

I am working on a project with the STM32F411 microcontroller. It is set in SPI slave mode and receives data without any problems. When I want to send data over the spi peripheral i works sometimes but most of the time the bits I am trying to send a shifted or there is wrong data sent. I have configured the spi peripheral like it was shown in an example in the standard peripheral drivers for this controller and I also don´t have a chip select line because I only have one slave in the system.

Is there something wrong in my setup or do i refill the tx buffer at a wrong moment?

Here is my code:

void spi1_init(){
SPI_InitTypeDef  SPI_InitStruct;

spi1_gpio_init();

// Enable the SPI periph clock
RCC_APB2PeriphClockCmd(RCC_APB2ENR_SPI1EN, ENABLE);

// Set data size to 8b 
SPI_InitStruct.SPI_DataSize = SPI_DataSize_8b;

SPI_I2S_DeInit(SPI1);
SPI_InitStruct.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64; // 100MHz / 64 = 1.5625MHz
SPI_InitStruct.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
SPI_InitStruct.SPI_FirstBit = SPI_FirstBit_MSB;
SPI_InitStruct.SPI_Mode = SPI_Mode_Slave;
SPI_InitStruct.SPI_NSS = SPI_NSS_Soft;
SPI_InitStruct.SPI_CRCPolynomial = 7;

// Mode 0 
SPI_InitStruct.SPI_CPOL = SPI_CPOL_Low;
SPI_InitStruct.SPI_CPHA = SPI_CPHA_1Edge;


// Init SPI 
SPI_Init(SPI1, &SPI_InitStruct);


//---------------------------------------------------------------------

spi1_interrupt_init();

//---------------------------------------------------------------------


   // Enable the SPI peripheral 
   SPI_Cmd(SPI1, ENABLE); 

 }


void spi1_gpio_init(void){
GPIO_InitTypeDef GPIO_InitStruct;

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);

GPIO_PinAFConfig(GPIOB, GPIO_PinSource3, GPIO_AF_SPI1);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource4, GPIO_AF_SPI1);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource5, GPIO_AF_SPI1);

GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_DOWN;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_3;
GPIO_Init(GPIOB, &GPIO_InitStruct);

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_4;
GPIO_Init(GPIOB, &GPIO_InitStruct);

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5;
GPIO_Init(GPIOB, &GPIO_InitStruct);
}

void spi1_interrupt_init(void){
NVIC_InitTypeDef  NVIC_InitStruct;

// Configure the SPI interrupt priority 
NVIC_InitStruct.NVIC_IRQChannel = SPI1_IRQn;
NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStruct);

// Enable the Rx buffer not empty interrupt 
SPI_I2S_ITConfig(SPI1,SPI_I2S_IT_RXNE,ENABLE);

 // Enable the Tx empty interrupt 
SPI_I2S_ITConfig(SPI1, SPI_I2S_IT_TXE, ENABLE);
}


void SPI1_IRQHandler(void)
{  
int8_t CmdReceived;
static uint32_t CmdCount = 0;
static int8_t RecArray[SPI_REC_BYTES];
static uint32_t dataCounter = 0;

    // SPI in Transmitter mode 
  if (SPI_I2S_GetITStatus(SPI1, SPI_I2S_IT_TXE) == SET)
 {
    SPI_I2S_SendData(SPI1, 123);

 }

 // SPI in Slave Receiver mode--------------------------------------- 
  if (SPI_I2S_GetITStatus(SPI1, SPI_I2S_IT_RXNE) == SET)
 {
 CmdReceived = SPI_ReceiveData(SPI1);

        if(CmdReceived < -100){
            CmdCount = 0;
            RecArray[CmdCount] = CmdReceived;



        } else if(++CmdCount < SPI_REC_BYTES){

            RecArray[CmdCount] = CmdReceived;

            if(CmdCount == (SPI_REC_BYTES-1)){
                callbackfunction(RecArray);
            }
        }


  }


 }