MY SPI receive buffer always returns 0xFF

Question

I am trying to interface SST26 with Pic32MX470F using Microchip Harmonyv 2.02b SPI drivers. I am able to write/ read correctly according to what I see on my logic analyzer as both MISO and MOSI lines show me the correct data.

The problem I am facing is that in my RX buffer I am not getting the correct data and only see 0xFF in it.

In addition to the read /write functions. I also do global unlock, block erase and write enable before writing anything. I also make sure that SDI line is set as input from harmony pin configuration. My SDI pin is connected to pin45(RPD11/PMCS1/RD11) on pic32.

Below is my implementation.

void Flash1_TestWrite()

{ 
    uint32_t num_of_bytes, loop, dataCount;

    flashData.TXbuffer[0] = 0x02; // Write Flash Page1 address 0x0000
    flashData.TXbuffer[1] = 0x00;
    flashData.TXbuffer[2] = 0x00; 
    flashData.TXbuffer[3] = 0x00;

    dataCount = 4;

    for(loop =0; loop < 20; loop ++)
    {
        flashData.TXbuffer[dataCount++] = 0xAA;
    }

    num_of_bytes = dataCount; //opcode + address + data

    Flash1_WREN(); / /Enable Write

    nFlashCS1Off();
    Flash1_Write_Buffer_Handle = DRV_SPI_BufferAddWrite(SPIHandle,(SPI_DATA_TYPE *) &flashData.TXbuffer[0], num_of_bytes, 0, 0);
   if (DRV_SPI_BUFFER_EVENT_COMPLETE & DRV_SPI_BufferStatus(Flash1_Write_Buffer_Handle)) 
   {
      nFlashCS1On();
   }
}



voidFlash1_Read( void )
{
    switch(flashData.state)
    {
        uint32_t num_of_bytes, loop, dataCount;

        case FLASH1_INIT:
        { 
             nFlashCS1On();
             flashData.state = FLASH1_SEND_READ_CMD;
            break;
        }
        case FLASH1_SEND_READ_CMD:
        { 
            flashData.TXbuffer[0] = 0x03; // Read Page 
            flashData.TXbuffer[1] = 0x00; 
            flashData.TXbuffer[2] = 0x00; // Address - MSB 
            flashData.TXbuffer[3] = 0x00; // Address - LSB 

            dataCount = 4;

            for(loop =0; loop < 20; loop ++)
            {
                flashData.TXbuffer[dataCount++] = 0xFF; // dummy bytes
            }

            num_of_bytes = dataCount;
            nFlashCS1Off();

            Flash1_Write_Buffer_Handle = DRV_SPI_BufferAddWrite(SPIHandle, (SPI_DATA_TYPE *) &flashData.TXbuffer[0], num_of_bytes, 0, 0);

            flashData.state = FLASH1_WAIT_FOR_REPLY;
            break;
        }

        case FLASH1_WAIT_FOR_REPLY: 
        {
            if(DRV_SPI_BUFFER_EVENT_COMPLETE &
                               DRV_SPI_BufferStatus(Flash1_Write_Buffer_Handle))
            flashData.state = FLASH1_GET_DATA;
            break;
        }

      case FLASH1_GET_DATA: 
        {
            Flash1_Read_Buffer_Handle = DRV_SPI_BufferAddRead( SPIHandle, (SPI_DATA_TYPE *) &flashData.RXbuffer[0], 24, 0, 0);
           flashData.state = FLASH1_WAIT_FOR_DATA;
           break; 
        }

      case FLASH1_WAIT_FOR_DATA: 
        { 
            if(DRV_SPI_BUFFER_EVENT_COMPLETE &
                               DRV_SPI_BufferStatus (Flash1_Read_Buffer_Handle))
            {
                nFlashCS1On(); // Assert CS line
                flashData.state = FLASH1_READ_COMPLETE;
            }
           break;
        }

      case FLASH1_READ_COMPLETE:
      {
        break; 
      }

      default:
        break;
    }
    return false;
}

Can someone suggest how I can get the correct data in my rx buffer?

When using SPI, always suspect "clock skew". That is, double-check your CPOL (clock polarity) and CPHA (clock phase) settings. — Lundin
Looks like it might be sending out too many clock signals. Is the for(loop =0; loop < 20; loop ++) { flashData.TXbuffer[dataCount++] = 0xFF; // dummy bytes } really necessary? Isn't the clocking for the read done in DRV_SPI_BufferAddRead? — pm101
Yes, but I added the dummy bytes for testing as it was still giving me 0xFF without the dummy bytes. — abdullah

abdullah abdullah · Accepted Answer · 2019-04-30T17:59:55

Atlast resolved the issue, turns out the SDI port on two different PIC32s were faulty. The third one that we got today worked.

Reminder to others: If your output and subsequent input over MOSI and MISO looks good, your clock looks correct, your pins are being set OK but you're not getting data, you might just have a faulty input connection on your chip.

Configuring the SDI pin as Open drain from Microchip harmony and also declaring the buffer as coherent was helpful atleast in our configuration.

MY SPI receive buffer always returns 0xFF

1 Answers