How to set up the DAC on arduino due for external triggering (DATRG)

[dirkboon]

Hi there,

I am using an arduino DUE, and I would like to "Arm" its DAC using a hardware trigger. My use case would be that the arduino receives a trigger from a clock which runs the rest of the setup. As soon as it receives it, it changes the output voltage of the DAC according to some precalculated value. The clock has a period of 9 us, so we have some time to waste, but not that much time.

The most simple way would be to connect an interrupt to a trigger input pin, and then change the output, but that leads to quite some jitter on the output port, so I hope that setting up the hardware properly will make it more stable.

The datasheet seems to suggest that it may be possible to use an external trigger (https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-11057-32-bit-Cortex-M3-Microcontroller-SAM3X-SAM3A_Datasheet.pdf, page 5)

According to the pinout, the DA trigger it should be accessible under pin D19 (https://docs.arduino.cc/resources/pinouts/A000056-full-pinout.pdf, in the "advanced" section, page 5)

I am guessing it would be a small adoption from this code, (thank you @anatolyk69_gmail.c ), but I don't understand what to change here:

void TC_setup ()
{
  pmc_enable_periph_clk(TC_INTERFACE_ID + 0 *3 + 0); 

  TcChannel * t = &(TC0->TC_CHANNEL)[0];            
  t->TC_CCR = TC_CCR_CLKDIS;                        
  t->TC_IDR = 0xFFFFFFFF;                           
  t->TC_SR;                                         
  t->TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK1 |          
              TC_CMR_WAVE |                         
              TC_CMR_WAVSEL_UP_RC |                 
              TC_CMR_EEVT_XC0 |     
              TC_CMR_ACPA_CLEAR | TC_CMR_ACPC_CLEAR |
              TC_CMR_BCPB_CLEAR | TC_CMR_BCPC_CLEAR;
  
  t->TC_RC = freq_intc;
  t->TC_RA = freq_intc /2;       
  t->TC_CMR = (t->TC_CMR & 0xFFF0FFFF) | TC_CMR_ACPA_CLEAR | TC_CMR_ACPC_SET; 
  t->TC_CCR = TC_CCR_CLKEN | TC_CCR_SWTRG;    
}

void dac_setup ()
{
  pmc_enable_periph_clk (DACC_INTERFACE_ID) ; // start clocking DAC
  dacc_reset(DACC);
  dacc_set_transfer_mode(DACC, 0);
  dacc_set_power_save(DACC, 0, 0);
  dacc_set_trigger(DACC, 1); /* PROBABLY HERE, but what should I do? */
  dacc_set_channel_selection(DACC, 1);
  dacc_enable_channel(DACC, 1);
  dacc_set_analog_control(DACC, DACC_ACR_IBCTLCH0(0x02) | DACC_ACR_IBCTLCH1(0x02) | DACC_ACR_IBCTLDACCORE(0x01));

  NVIC_DisableIRQ(DACC_IRQn);
  NVIC_ClearPendingIRQ(DACC_IRQn);
}

Would anyone be able to point out how do do this?

If it's unclear what I would like to do, I can also make a small sketch.

kind regards,

Dirk

[florence023]

Hello, @dirkboon

To "arm" the DAC on your Arduino Due using a hardware trigger, follow these steps:

Set up the Timer/Counter (TC) to generate the trigger:

void TC_setup ()
{
  pmc_enable_periph_clk(TC_INTERFACE_ID + 0 * 3 + 0); 
  TcChannel * t = &(TC0->TC_CHANNEL)[0];            
  t->TC_CCR = TC_CCR_CLKDIS;                        
  t->TC_IDR = 0xFFFFFFFF;                           
  t->TC_SR;                                         
  t->TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK1 |          
              TC_CMR_WAVE |                         
              TC_CMR_WAVSEL_UP_RC |                 
              TC_CMR_EEVT_XC0 |     
              TC_CMR_ACPA_CLEAR | TC_CMR_ACPC_CLEAR |
              TC_CMR_BCPB_CLEAR | TC_CMR_BCPC_CLEAR;
  t->TC_RC = 10000;   // Adjust frequency as needed
  t->TC_RA = 5000;    // Adjust to half period
  t->TC_CCR = TC_CCR_CLKEN | TC_CCR_SWTRG;
}

Configure the DAC to use the external trigger:

void dac_setup ()
{
  pmc_enable_periph_clk(DACC_INTERFACE_ID);
  dacc_reset(DACC);
  dacc_set_transfer_mode(DACC, 0);
  dacc_set_power_save(DACC, 0, 0);
  dacc_set_trigger(DACC, 1); // Enable hardware trigger
  DACC->DACC_MR |= DACC_MR_TRGEN_EN | DACC_MR_TRGSEL(0); // Use TIOA0 as trigger
  dacc_set_channel_selection(DACC, 1);
  dacc_enable_channel(DACC, 1);
  dacc_set_analog_control(DACC, DACC_ACR_IBCTLCH0(0x02) | DACC_ACR_IBCTLCH1(0x02) | DACC_ACR_IBCTLDACCORE(0x01));
}

This sets up TC0 to generate a trigger signal and configures the DAC to respond to this trigger, allowing it to change the output voltage based on the external clock signal.

Best Regard,
florence023

[dirkboon]

Hi Florence023,

Thank you very much for the code! But if I understand correctly what you do, you generate a trigger on the arduino itself, right? In this line:

DACC->DACC_MR |= DACC_MR_TRGEN_EN | DACC_MR_TRGSEL(0); // Use TIOA0 as trigger

In my case, it's a true external trigger, as in one that is generated by a signal generator. So it's probably even easier to do, right? But what would the command be here?

[dirkboon]

In case anyone is wondering, I found out that it's relatively simple. The commands can be found here.

To configure the DAC to listen to a hardware trigger (on pin 19), just use:

 dacc_set_trigger(DACC_INTERFACE, 0);

To configure it to output immediately, just use

  dacc_disable_trigger(DACC_INTERFACE);