Buffers, pointers and SPI call

Using Arduino Programming Questions
1

I am attempting to convert some software written for the DWM3000 to arduino
and am getting a little lost in the program and the necessary SPI commands to talk to the unit.

This is a stripped down call sequence in the program I am converting.

First Question
The links between the subroutines using pointers to return data.

dwt_read32bitoffsetreg sets uint8_t buffer[4];
dwt_readfromdevice links this as uint8_t *buffer (a pointer)
dwt_xfer3000 also links this as uint8_t *buffer (a pointer)
readfromspi links this as uint8_t *readBuffer (a pointer)

Can someone please explain this, as the readbuffer has to eventually end up as 4 bytes in buffer

Second question
dwt_xfer3000 sets uint8_t header[2];
readfromspi links this as uint8_t *headerBuffer (a pointer)
Does this command send both header bytes?
SPI.transfer((uint8_t *)headerBuffer); // Send header

Third question
How to I get the results from an SPI read into buffer, back through the pointer system

Any assistance gratefully received. This software is doing my head in

uint32_t dwt_readdevid(void)        
{
return dwt_read32bitoffsetreg(DEV_ID_ID,0)            
}

uint32_t dwt_read32bitoffsetreg (int regFileID, int regOffset)                                  
{
uint8_t buffer[4];
dwt_readfromdevice(regFileID,regOffset,4,buffer);    // Read 4 bytes (32-bits) register into buffer
}

void dwt_readfromdevice (uint32_t regFileID, uint16_t index, uint16_t lengthA, uint8_t *buffer)   
{
dwt_xfer3000(regFileID, index, lengthA, buffer, DW3000_SPI_RD_BIT);
}

void dwt_xfer3000 (const uint32_t regFileID,const uint16_t indx,const uint16_t lengthA, uint8_t *buffer, const spi_modes_e mode)
  {
   uint8_t  header[2];           // Buffer to compose header in
   uint16_t cnt = 0;             // Counter for length of a header
   ////cnt and header populated
   readfromspi(cnt, header, lengthA, buffer);
  }

int readfromspi(uint16_t headerLength,uint8_t *headerBuffer,uint16_t readlength,uint8_t *readBuffer)
{
  SPI.transfer((uint8_t *)headerBuffer);                 // Send header
  // how do I get the read from SPI
return 0;
}
2

That code does not make sense. SPI::transfer() sends 1 byte, not a pointer to data. I would suggest looking at the SPI examples that come with the library. They show how to read/write registers on a device. (File->examples->SPI->.....)

3

Nope, if you use the correct overload, you can send a whole buffer. From SPI.h for Uno board package:

  inline static void transfer(void *buf, size_t count) {
    if (count == 0) return;
    uint8_t *p = (uint8_t *)buf;
    SPDR = *p;
    while (--count > 0) {
      uint8_t out = *(p + 1);
      while (!(SPSR & _BV(SPIF))) ;
      uint8_t in = SPDR;
      SPDR = out;
      *p++ = in;
    }
    while (!(SPSR & _BV(SPIF))) ;
    *p = SPDR;
  }

That not withstanding, OP's question is unintelligible.

4

But the OP did not specify a length, so that function signature does not match. I see no default for the length being 1, so.....

still does not make sense.

5

Okay, then what should the SPI send be?

6

Look at the examples that come with the SPI library as I pointed out in reply #2

7

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