I am testing the timers 1 and 2 on an arduino UNO with ISR.
I connected a probe of my oscilloscope to the PIN A5, and the PIN A5 is toggled if the ISR is "slow" to be executed.
Firstly I tested timer 1 in FAST PWM mode and prescaler at 1.
void setup() {
// Configuration of Pin connected to oscilloscope
DDRC |= B00100000; // set pin A5 as digital output
PORTC &= B11011111; // set pin A5 low
// configuration of Timer 1
TCCR1A = 0x03; // PWM Fast mode selected
TCCR1B = 0x01; // No prescaler --> 16Mhz
OCR1A = 200; // Set OCR1A at 200
TIMSK1 = 0x02; // interrupt on compare match with OCR1A, so when TCNT1 = 200 we enter in ISR
}
void loop() {
// put your main code here, to run repeatedly:
}
ISR (TIMER1_COMPA_vect) {
// Normaly we should not enter in this statement because ISR should be run when TCNT1 >= 200
if (TCNT1 > 0 && TCNT1 <200)
{
// toggle of A5 pin
PORTC |= B00100000;
PORTC &= B11011111;
}
TIFR1 |= B00000010; // clear interrupt flag
}
The result of PIN A5 to the oscilloscope is in the attached file (see Test_Timer_1)
And I did the same test with Timer 2
Here is the code
void setup() {
// Configuration of Pin connected to oscilloscope
DDRC |= B00100000; // set pin A5 as digital output
PORTC &= B11011111; // set pin A5 low
// configuration of Timer 2
TCCR2A = 0x03; // PWM Fast mode selected
TCCR2B = 0x01; // No prescaler --> 16Mhz
OCR2A = 200; // Set OCR2A at 200
TIMSK2 = 0x02; // interrupt on compare match with OCR2A, so when TCNT2 = 200 we enter in ISR
}
void loop() {
// put your main code here, to run repeatedly:
}
ISR (TIMER2_COMPA_vect) {
// Normaly we should not enter in this statement because ISR should be run when TCNT2 >= 200
if (TCNT2 > 0 && TCNT2 <200)
{
// toggle of A5 pin
PORTC |= B00100000;
PORTC &= B11011111;
}
TIFR2 |= B00000010; // clear interrupt flag
}
And the result of pin A5 with the oscilloscope (see Test_Timer_2) is in the attached file
void setup()
{
// Configuration of Pin connected to oscilloscope
DDRC |= B00100000; // set pin A5 as digital output
PORTC &= B11011111; // set pin A5 low
// configuration of Timer 1
TCCR1A = 0x00; //
TCCR1B = 0x09; //
OCR1A = 200; // Set OCR1A at 200
TIMSK1 = 0x02; // interrupt on compare match with OCR1A, so when TCNT1 = 200 we enter in ISR
}
void loop()
{
// put your main code here, to run repeatedly:
}
ISR (TIMER1_COMPA_vect)
{
// Normaly we should not enter in this statement because ISR should be run when TCNT1 >= 200
if (TCNT1 > 0 && TCNT1 < 200)
{
// toggle of A5 pin
PORTC |= B00100000;
PORTC &= B11011111;
}
TIFR1 |= B00000010; // clear interrupt flag
}
TIMER2
void setup()
{
// Configuration of Pin connected to oscilloscope
DDRC |= B00100000; // set pin A5 as digital output
PORTC &= B11011111; // set pin A5 low
// configuration of Timer 2
TCCR2A = 0x02; //
TCCR2B = 0x01; // No prescaler --> 16Mhz
OCR2A = 200; // Set OCR2A at 200
TIMSK2 = 0x02; // interrupt on compare match with OCR2A, so when TCNT2 = 200 we enter in ISR
}
void loop()
{
// put your main code here, to run repeatedly:
}
ISR (TIMER2_COMPA_vect)
{
// Normaly we should not enter in this statement because ISR should be run when TCNT2 >= 200
if (TCNT2 > 0 && TCNT2 < 200)
{
// toggle of A5 pin
PORTC |= B00100000;
PORTC &= B11011111;
}
TIFR2 |= B00000010; // clear interrupt flag
}
Thanks ! My mistake !
So I tested again by configuring correctly timer 1 in PWM FAST MODE and now I have the same thing for timer 1 and 2.
Every 1ms I am able to enter in the "if statement" in the ISR. So it means that sometimes it need more 50 clock cycles to reach the if statement after the interrupt.
But I don't know why because I am not doing anything else ! Any thought ?
I don't want to use CTC mode but PWM FAST MODE 8 bit.
My goal is to not enter in the if statement in the ISR.
Because OCR1A is set at 200. I thought that it was enough time to run completely the ISR function. But as you can see in my previous tests, sometimes TCNT1 has already been cleared and is between 0 and 200. And I don't know why because I don't do anything in this code.
