16 bit SPI on Arduino Due

Question

I'm trying to control AD7091-8 using Arduino Due.

This IC calls for 16 bit SPI R/W. I'd read that I can change the transmit and receive bits of Arduino DUE by changing a register (bits 4-7 of SPI_CSR).

I was able to change the SPI of Due from 8 to 16 bits. Confirmed this by looking at SCLK and MOSI in the scope. However, the data I want to transfer is becoming intermittent.

I want to send 0x1000. On 8 bits, using the line

SPI.transfer(10,0x10,SPI_LAST);

I really can see this being sent on MOSI.

However, when I'm on 16 bits, the line

SPI.transfer(10,0x1000,SPI_LAST);

It's either becoming 0x0000 or 0x0008. I'm losing the bit or it's becoming LSB_FIRST. Not MSB_FIRST.

Below is the actual code.

#include <SPI.h>
#include "C:\Users\Smart Surface 2\AppData\Local\Arduino15\packages\arduino\hardware\sam\1.6.11\system\CMSIS\Device\ATMEL\sam3xa\include\component\component_spi.h"
#include "C:\Users\Smart Surface 2\AppData\Local\Arduino15\packages\arduino\hardware\sam\1.6.11\system\CMSIS\Device\ATMEL\sam3xa\include\instance\instance_spi0.h"

#define CS 10

void setup() {

  pinMode(CONV,OUTPUT);

  Serial.begin(9600);
  SPI.begin(CS);
  SPI.setDataMode(CS, SPI_MODE0);
  SPI.setClockDivider(CS,21);  

  REG_SPI0_WPMR=0x53504900;
  REG_SPI0_CR=0x1;
  SPI0->SPI_CSR[0]=0x00001580; 

  SPI.setBitOrder(MSBFIRST);
  delay(1);
}

void loop() {

  SPI.transfer(CS,0x1000,SPI_LAST);

  int a = SPI.transfer(CS,0x0000, SPI_LAST);
  delay(1000);

  Serial.println(a);
}

How can I make my data reliable and the order still with MSB first?

Answer 1

Found the problem on the SPI library.

When I do the command SPI.transfer, the data is stored on a byte type variable. And I'm passing a 16 bit data on it.

I've changed line 84 of SPI.h to

uint16_t transfer(byte _pin, uint16_t _data, SPITransferMode _mode = SPI_LAST);

so it will return and receive 16 bit data.

Also have to change the corresponding function on SPI.cpp (line 174)

uint16_t SPIClass::transfer(byte _pin, uint16_t _data, SPITransferMode _mode)

so they will match.

I've copied and renamed the SPI library that I've changed so it won't affect other codes.