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Delay between SPI bytes

Question asked by holder.gary on May 7, 2014
Latest reply on May 7, 2014 by Clive One

Using STM3220G-EVAL with my serial FLASH added to board.

I am writing to a serial flash via the SPI port. My clock speed is 30Mhz. All is working fine, but I was expecting less delay between the SPI clock transfers. My code is shown below. The scope image shows a 700ns delay between clock tranfers. This is mostly cuaed by waiting for the RXNE bit to set. Since the received byte is clocked in as the transmit byte is clocked out I would expect minimal delay between byte transfers. In other word I would expect to see a continuous clock sequence during this transfer. Is this the delay I should expect or is there something in my setup that I can change to make the delay shorter?  (I tried to attach image of scope trace but your websight gave me Errors)



// SPI configuration

  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;// set to full duplex mode, separate MOSI and MISO lines

  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;                     // transmit in master mode, NSS pin has to be always high

  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;                 // one packet of data is 8 bits wide

  SPI_InitStructure.SPI_CPOL = SPI_CPOL_High;                       // the clock pin is set normally high

  SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;                      // data is clocked on the rising edge (2nd edge from normally high aka serial mode 3)

  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;                         // set the NSS management to internal software controlled

  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_2;// run the SPI clock as fast as possible

  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;                // data is transmitted MSB first

  SPI_InitStructure.SPI_CRCPolynomial = 7;

  SPI_Init(MX25L6406_SPI, &SPI_InitStructure);


  /// Enable SPI Peripheral

  SPI_Cmd(MX25L6406_SPI, ENABLE);



//Read flash ID function

//Enable Flash Chip Select



          while (SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_TXE) == RESET);         

          SPI_I2S_SendData(MX25L6406_SPI, 0x009F);


          while(SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_RXNE) == RESET) {}         



          while (SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_TXE) == RESET

          SPI_I2S_SendData(MX25L6406_SPI, 0x0000);


          while(SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_RXNE) == RESET) {}

          MX25L6406_ID_struct.manufacturer_ID = SPI_I2S_ReceiveData(MX25L6406_SPI);


          while (SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_TXE) == RESET);      

          SPI_I2S_SendData(MX25L6406_SPI, 0x0000);


          while(SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_RXNE) == RESET) {}

          MX25L6406_ID_struct.memory_type_ID = SPI_I2S_ReceiveData(MX25L6406_SPI);


while (SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_TXE) == RESET);      

          SPI_I2S_SendData(MX25L6406_SPI, 0x0000); 


          while(SPI_I2S_GetFlagStatus(MX25L6406_SPI, SPI_I2S_FLAG_RXNE) == RESET) {}      

       MX25L6406_ID_struct.memory_density_ID = SPI_I2S_ReceiveData(MX25L6406_SPI);      

    // Disable Flash Chip