I am using the quarto to output a waveform at 16 us update intervals and I am seeing a strange voltage drop at the beginning and end of the signal. I did verify that the values computed by the quarto do not have these spikes. While verifying I noticed that adding a "delay" in the form of calling Serial2.printf("%d,%f", time, out); fixes my spike so I am unsure of what is going on.

Strange waveform (see spikes at beginning and end of waveform):

Normal waveform (uses call to Serial2):

Code:

// GLOBAL CONTROLS
#define DAC_UPDATE 16 // DAC update interval [us]
#define PERIOD 4000 // Period of control cycle [us]
#define TRAP_TIME 2000 // Time for trapping [us]


// Common objects
IntervalTimer Timer;
int time = 0;


// Update DAC function
void updateDAC() {
	if (time < PERIOD) {
	        float out = cosPower(TRAP_TIME, 1, 8);

		writeDAC1(out);
		writeDAC2(out);

		// Enabling this gets rid of the spikes seen at the start and end of the signal
		// Serial2.printf("%d,%f\r\n", time, out);

		time += DAC_UPDATE;
	} else {
		time = 0;
	}
}

float cosPower(int trap_time, float amplitude, int power) {
	float out;
	if (time < trap_time) {
		out = - amplitude * pow(cos(PI * time / trap_time), power) + amplitude;
	} else {
		out = 0;
	}
	return out;
}

void setup() {
	Timer.begin(updateDAC, DAC_UPDATE);
}

void loop() {
}