int main(void)
{
/*!< At this stage the microcontroller clock setting is already configured,
this is done through SystemInit() function which is called from startup
file (startup_stm32f4xx.s) before to branch to application main.
To reconfigure the default setting of SystemInit() function, refer to
system_stm32f4xx.c file
*/
uint8_t d0 = 0xd9; // 11011001, test data0




// declare SPI init data structure
SPI_InitTypeDef spi2;

// declare GPIO init data structure
GPIO_InitTypeDef gpiob;

// enable SPI2 clock
RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI2, ENABLE);

// enable SPI2 pins
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);

// connecting Alternate Functions to GPIOB pins
GPIO_PinAFConfig(GPIOB, GPIO_PinSource13, GPIO_AF_SPI2);
GPIO_PinAFConfig(GPIOB, GPIO_PinSource15, GPIO_AF_SPI2);


// GPIOB configuration
gpiob.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_15;
gpiob.GPIO_Mode = GPIO_Mode_AF;
gpiob.GPIO_OType = GPIO_OType_PP;
gpiob.GPIO_Speed = GPIO_Speed_50MHz;
gpiob.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_Init(GPIOB, &gpiob);

// initializing the SPI2
SPI_I2S_DeInit(SPI2);
spi2.SPI_Direction = SPI_Direction_1Line_Tx;
spi2.SPI_DataSize = SPI_DataSize_8b;
spi2.SPI_CPOL = SPI_CPOL_High;
spi2.SPI_CPHA = SPI_CPHA_1Edge;
spi2.SPI_FirstBit = SPI_FirstBit_LSB;
spi2.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_8;
spi2.SPI_Mode = SPI_Mode_Master;

SPI_Init(SPI2, &spi2);


// enable the SPI2
SPI_Cmd(SPI2, ENABLE);

// sending the data
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
SPI_I2S_SendData(SPI2, (uint8_t)d0);



while (1)
{}
}