I2C Repeated Start

Hardware Arduino Due
24

Sure... It's more than you asked for, but here are some checking routines:
(Embiic is the name of the project this code was used in)

uint32_t I2C_Get_Status_Register(){
  return pTwi->TWI_SR;
}

boolean Embiic_Check_NACK(uint32_t sr) {
  return ((sr & TWI_SR_NACK) & TWI_SR_NACK);
}

boolean Embiic_Check_TXCOMP(uint32_t sr) {
  return ((sr & TWI_SR_TXCOMP) == TWI_SR_TXCOMP);
}

boolean Embiic_Wait_ACK_TXCOMP() {
  unsigned long start, now;
  uint32_t sr, tw_nack, tw_txcomp;
  
  tw_txcomp = 0;
  start = micros();
  
  while (tw_txcomp == 0) {
    sr = I2C_Get_Status_Register();
    now = micros();
    if (now < start) {  // handle overflow, at at the expense of a longer timeout
      start = now;
      now++;
    } else {
      now = now - start;
    }
    if (now > I2C_ACK_TIMEOUTuS){
      DBG_PRINTLN("Embiic_CheckTXCOMP: Timeout.");
      I2C_Reset_Request = 1;
      return false;
    }
    tw_nack = Embiic_Check_NACK(sr);
    if (tw_nack != 0) {
      DBG_PRINTLN("Embiic_CheckTXCOMP: NACK. Natch.");
      return false;
    }
    tw_txcomp = Embiic_Check_TXCOMP(sr);
  }
  return true;
}

boolean Embiic_Wait_TXCOMP() {
  unsigned long start, now;
  uint32_t sr, tw_txcomp;
  
  tw_txcomp = 0;
  start = micros();
  
  while (tw_txcomp == 0) {
    sr = I2C_Get_Status_Register();
    now = micros();
    if (now < start) {  // handle overflow, at at the expense of a longer timeout
      start = now;
      now++;
    } else {
      now = now - start;
    }
    if (now > I2C_ACK_TIMEOUTuS){
      DBG_PRINTLN("Embiic_CheckTXCOMP: Timeout.");
      I2C_Reset_Request = 1;
      return false;
    }
    tw_txcomp = Embiic_Check_TXCOMP(sr);
  }
  return true;
}

boolean Embiic_WaitByteSent() {
  uint32_t sr;
  //bad: TXCOMP is 1, NACK is 1
  unsigned long start, now;
  start = micros();
  while (1) {
    now = micros();
    if (now < start) {  // handle overflow, at at the expense of a longer timeout
      start = now;
      now++;
    } else {
      now = now - start;
    }
    if (now > I2C_ACK_TIMEOUTuS){
      DBG_PRINTLN("Embiic_WaitByteSent: Timeout.");
      I2C_Reset_Request = 1;
      return false;
    }
    sr = I2C_Get_Status_Register();
    if ((sr & TWI_SR_NACK) & TWI_SR_NACK) {
      DBG_PRINTLN("Embiic_WaitByteSent: NACK. Bad Address?");
      return false;
    }
    if ((sr & TWI_SR_TXRDY) == TWI_SR_TXRDY) {
      return true;
    }
  }
  return true;
}

boolean Embiic_WaitByteReceived() {
  unsigned long start, now;
  start = millis();
  while (!TWI_ByteReceived(WIRE_INTERFACE)) {
    now = millis();
    if (now < start) {  // handle overflow, at at the expense of a longer timeout
      start = now;
      now++;
    } else {
      now = now - start;
    }
    if (now > I2C_READ_TIMEOUTmS){
      DBG_PRINTLN("Embiic_WaitByteReceived: Timeout.");
      I2C_Reset_Request = 1;
      return false;
    }
  }
  return true;
}

-Chris
I'm not a coder. I just play one on the internets.