Electronic – Arduino and Interrupts: Fast way to get pin values

arduinocinterrupts

I use an Arduino Uno and already set it up to work with interrupts on digital pins 2, 3, 4 and 5 according to an explanation1 I found.

void setup() contains the following code to setup the interrupts.

  //Endable Interrupts for PCIE2 Arduino Pins (D0-7)
  PCICR |= (1<<PCIE2);

  //Setup pins 2,3,4,5
  PCMSK2 |= (1<<PCINT18);
  PCMSK2 |= (1<<PCINT19);
  PCMSK2 |= (1<<PCINT20);
  PCMSK2 |= (1<<PCINT21);

  //Trigger Interrupt on rising edge
  MCUCR = (1<<ISC01) | (1<<ISC01);

And now, the ISR( PCINT2_vect ) function is triggered on every interrupt. That works like a charm. My question is, what is the best/fastest way to find out, which pin was triggered?

I found something in Re: Is better to use ISR(PCINT2_vect) or attachInterrupt on pins 2, 3?, but I do not understand the code and it does not work out of the box. But it looks impressive…

What is the solution?

[2] http://arduino.cc/forum/index.php/topic,72496.15.html#lastPost

Edit:

At the moment, I am reading the pin state from the from the input pin register:

  if (PIND & 0b00000100)
    Serial.println( "PIN 2" );
  if (PIND & 0b00001000)
    Serial.println( "PIN 3" );
  if (PIND & 0b00010000)
    Serial.println( "PIN 4" );
  if (PIND & 0b00100000)
    Serial.println( "PIN 5" );

In the end, I want to count the interrupts on the pins.
But how can I assure, that there are no counted twice?

Best Answer

I have a first solution myself, but i could not test the reliability as the hardware is not finished jet.

First I added oldPins and tickCount as global variables:

static byte oldPins = 0;
volatile unsigned int tickCount[4] = { 0, 0, 0, 0 };

And thats how I solved the ISR at the moment. Better solutions are more than welcome.

ISR( PCINT2_vect ) {
  //Read values from digital pins 2 to 7
  const byte actPins = PIND;
  //Match this values agaist the oldPins bitmask (XOR and AND for raising edge)
  const byte setPins = (oldPins ^ actPins) & actPins;

  if (setPins & 0b00000100)
    tickCount[0]++;
  if (setPins & 0b00001000)
    tickCount[1]++;
  if (setPins & 0b00010000)
    tickCount[2]++;
  if (setPins & 0b00100000)
    tickCount[3]++;

  oldPins = actPins;
}

Related Solutions

Electronic – dsPIC33, SPI slave, and Timer1 interrupts. What happens

Normally you would set up the SPI peripheral once, then leave it on. The extra handshaking you are doing is preventing you from using the hardware to its full capability. Also doing a busy wait for the master to assert slave select is a bad idea if you ever want the processor to do something else.

Since you are transferring 16 bits of less per message, I would just let the hardware take care of it. Then you can monitor the SPI interrupt flag to determine when new data has been received from the master. If you need to slow down the master for flow control reasons, I would do that outside of the SPI message. I suspect the interrupt is adding latency to your home grown handshaking scheme, and something somewhere isn't quite right and can't tolerate that latency. That's assuming of course that the interrupt doesn't try to touch the SPI hardware or any of its I/O lines.

Electronic – arduino – AttatchInterrupt Constantly interrupts

As you've determined that kind of receiver will have a PWM output to control a servo, the Wikipedia Servo Control article has some good information about it. If you wanted to use it anyway the normal neutral position will be 1.5mS so you could use something like the following code that uses the pulseIn function to treat a pulse of 1.75mS or longer as being on:

#define MY_PIN 0

void setup() {
    Serial.begin(9600);
    pinMode(MY_PIN, INPUT);
}

void loop() {
   if (pulseIn(MY_PIN, HIGH) >= 1750)
      Serial.println("TX on");        
}

Note that the typical period between pulses is 20mS so your code will be stalled in pulseIn for around that period. If that's a problem you could go back to using the interrupt and set it for CHANGE and keep track of the time between when the line goes high and low again. It would be something like the following untested code:

#define MY_PIN 0 // Make sure this matches the interrupt line
unsigned long start_micros = 0;
unsigned long last_duration = 0;

void setup() {
    Serial.begin(9600);
    pinMode(MY_PIN, INPUT);
    attachInterrupt(0 , PWM_handler, CHANGE);
}

void loop() {
   if (last_duration >= 1750)
      Serial.println("TX on");        
}

void PWM_hander()
{
    if (digitalRead(MY_PIN) == HIGH)
        start_micros = micros();
    else
        last_duration = micros() - start_micros;
}

Best Answer

Related Solutions

Electronic – dsPIC33, SPI slave, and Timer1 interrupts. What happens

Electronic – arduino – AttatchInterrupt Constantly interrupts

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