I work on an Arduino Uno.
For setting up a PWM signal I use fast PWM.
#define MY_MEASURE1 20
#define MY_MEASURE2 200
...
...
void pwmSignal() {
// 16 bit Timer Counter 1
TCCR1A = (0 << COM1A1) + (1 << WGM11);
TCCR1B = (1 << WGM13) + (1 << WGM12) + (1 << CS12);
ICR1 = MY_TOP;
OCR1A = MY_BOTTOM;
OCR1B = MY_MEASURE1; // for analog measurement
DDRB |= (1 << DDB1);
TIMSK1 |= (1 << OCIE1B);
}
Generation of PWM on Port 9 is OK. It generates a signal with 1ms duty cycle, based on OCR1A and ICR1. -> ok
Additionally I want to do an analog measurement when counter reaches MY_MEASURE1 (see code). For this I use OCR1B: An interrupt service routine is triggered when there is the compare match for OCR1B. -> also ok.
But now I want to execute an additional analog measurement in the same cycle when counter reaches MY_MEASURE2. For this, I change OCR1B value directly within the ISR:
This ISR is just for examining the problem:
int iread = 0;
ISR(TIMER1_COMPB_vect) {
switch (iread) {
case 0:
iread = 1;
adc1 = adc;
OCR1B = MY_MEASURE2;
digitalWrite(check, 1);
analogRead(stromAnalog);
digitalWrite(check, 0);
break;
case 1:
iread = 0;
adc2 = adc;
OCR1B = MY_MEASURE1;
digitalWrite(check, 1);
analogRead(stromAnalog);
digitalWrite(check, 0);
break;
}
}
Note: The digitalWrite is to produce a test output to see whats happens. It is the second trace line in the following image.
The problem is: There is only one measurement during a PWM cycle. The change in OCR1B takes place only at the next cycle so I have alternate measurements at MY_MEASURE1, MY_MEASURE2, but only with one per cycle and not twice.
I would expect compare match interrupt twice within a cycle. Instead I get this:
You see, A and B will occur alternately, but not in the same cycle.
Where is the problem??
