timer interrupts on ATtiny x4

Other Hardware 3rd Party Boards
1

Hello,

I am trying to figure if the high level on INT0 is longer or shorter than 70us :

1 bit
<- 50us ->
XXXXXXXX____________

0 bit
<- 100us ->
XXXXXXXXXXXXXXXX___

^
70 us detection

In order to detect the rising edge, I have set up the interrupt on INT0 :

ISR(INT0_vect){
  // to be coded
}

void setup(){
  cli();                                         // disable interrupts during setup
  MUCUR|=(1<<ISC00)|(1<<ISC01);  // setting interrupt on rising edge of INT0
  GIMSK|=(1<<INT0);                     // enable interrupt on INT0
  sei();                                         // Global interrupt enable
}

I know want to set a timer interrupt 70us after the external interrupt. I have no idea of how to implement it.

2

What you want to do is use Timer1 in "Input capture" mode, it is designed for measuring pulse lengths like this.

3

Yes, when I detect the rising edge I can put the timer 1 (TCNT1) at 0, and I can compare it to OCR1A.

But how can I activate the timer interruption ?

I have found a solution with the overflow interrupt :
I set the overflow interrupt (setting the first bit of TIMSK1) and put TCNT1 (counter) to a certain value when I detect the rising edge, then I am able to detect the overflow and clear the first bit of TIMSK1.

Do you think that it would be better to use a comparison (with OCR1A for example) ?

Thank you for your answer which gives me the name for searching

4

Tutorial on Timers and Input Capture mode (scroll down the page for Input Capture).