Go Down

Topic: Is this too big for ISR ? (Read 1 time) previous topic - next topic

FardinB

Oct 11, 2012, 12:24 am Last Edit: Oct 11, 2012, 12:27 am by FardinB Reason: 1
Hi, I was wondering if this ISR is too much for processing power of Arduino?

The interrupt is set at 1kHz
Code: [Select]

ISR(TIMER1_COMPA_vect) {  //Interrupt at freq of 1kHz
 distance = getDistance(Lsensor);
 pressure = getPressure(Psensor);
 prSwitch = getPswitch(Pswitch);
 temp = getTemperature(tmp);
 Fldtemp = getTemperature(Fluidtmp);
 
 Serial.print(drive);
 Serial.print(" ");
 Serial.print(distance);
 Serial.print(" ");
 Serial.print(pressure);
 Serial.print(" ");
 Serial.print(prSwitch);
 Serial.print(" ");
 Serial.print(temp);
 Serial.print(" ");
 Serial.println(Fldtemp);
}

And here are the function calls in the ISR:
Code: [Select]

int getPressure(const int pin) {
 float ADCpressure = analogRead(pin);
 ADCpressure = (ADCpressure/1023)*25;
 return (int) ADCpressure;
}

int getPswitch(const int pin) {
 if(digitalRead(pin) == HIGH)
 {
   return 1;
 }
 if(digitalRead(pin) == LOW)
 {
   return 0;
 }
}

int getTemperature(const int pin) {
  float ADCtemperature = analogRead(pin);
  ADCtemperature = ADCtemperature/1.023;
  return (int) ADCtemperature;
}

int getDistance(const int pin) {
  return analogRead(pin);
}


Any ideas on how to make this work?

Nick Gammon

It's nothing to do with processing power. Don't do Serial.print inside an ISR.

http://www.gammon.com.au/interrupts

Nick Gammon

Just set a flag, test it in loop, and do your readings and displays there.

FardinB

I need to send these data every millisecond to the PC.

Any help is appreciated

Thanks

Nick Gammon


FardinB


KeithRB

Haven't you done the math yet?

115200 baud = 115200 bits per second
= 11520 bytes per second
= 11.5 bytes per millisecond

You can't send that many characters in the 1 mS time frame, it has nothing to do with the "processing power" of the Arduino, but the baud rate.

FardinB

I am sorry i did not see the last reply you posted.
Is there a way to increase the baud rate then. increase it in a way that PC can receive it?

Nick Gammon

You are getting close to the maximum. How about not sending the spaces? Even then you will be pushing it to condense your data into 11 bytes.

A more reasonable approach might be to do some calculations and send an average every second, or a delta (eg. rather than the temperature, the change in temperature).

KeithRB

You might have to send it as binary instead of characters. That way, for example, 0xFF saves on one character over 255.

How long do all your readings take? that might be more than a millisecond right there!

WizenedEE

I managed to get 460800 baud with the uno. Above that, I would just see garbage.

You could also use Serial.write rather than print so you just print 2 bytes rather than somewhere between one and six (and you'd save another because you wouldn't need a deliminator). Then you'd have to write a program on your computer to interpret it, though

KeithRB

According to this:
http://www.arduino.cc/en/Reference/AnalogRead

An analog read takes .1 mS, so your three Analog reads take 30% of your 1 mS anyway.

FardinB

I optimized my analogRead to get the maximum speed out of it.
This page (near the bottom) shows you how to get 77 kHz reading speed out of analog read. So the analog read times is not a concern to me.
https://sites.google.com/site/measuringstuff/the-arduino

@WizenedEE
How did you manage to read that speed on the serial monitor of PC?


WizenedEE


@WizenedEE
How did you manage to read that speed on the serial monitor of PC?

Code: [Select]

screen /dev/ttyACM0 460800

I run GNU/linux

FardinB

How about this code for ISR? would it run faster?

Code: [Select]

ISR(TIMER1_COMPA_vect) {  //Interrupt at freq of 250Hz
  distance = getDistance(Lsensor);
  pressure = getPressure(Psensor);
  prSwitch = getPswitch(Pswitch);
  temp = getTemperature(tmp);
  Fldtemp = getTemperature(Fluidtmp);
 
  toprint = 0; //reset buffer
  toprint += drive;
  toprint += ' ';
  toprint += distance;
  toprint += ' ';
  toprint += pressure;
  toprint += ' ';
  toprint += prSwitch;
  toprint += ' ';
  toprint += temp;
  toprint += ' ';
  toprint += Fldtemp;
 
  Serial.println(toprint);
}


Go Up