Chief Delphi - Reading interupt pin as Standard IO

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Reading interupt pin as Standard IO

I am trying to generate code that reads the pulswidth of a signal. I am avoiding use of Interupt pins 1 and 2 for later use. As my code is set up, I am trying to read the pulsewidth on pin 3. (BTW this is the Vex controller, I don't think it should make a difference though)
The code:

Code:

#define accel_x                rc_dig_int3



.......

  else if (INTCONbits.RBIF && INTCONbits.RBIE)  /* Ints 3-6 (RB4, RB5, RB6, or RB7) changed. */

  {

    int_byte = PORTB;          /* You must read or write to PORTB */

        if(accel_x){

                WriteTimer1( 0x00 );

                T1CONbits.TMR1ON = 1; // turn it on

        }

        else if (!accel_x){

                        T1CONbits.TMR1ON = 0; // turn it off

                        accel_xTilt= ReadTimer1();

                        WriteTimer1( 0x00 );

                }

        



    INTCONbits.RBIF = 0;     /*     and clear the interrupt flag         */

  }

I had a suspicion that maybe I am reading the pin incorrectly, so I set up:

Code:



void Process_Data_From_Local_IO(void){

if(accel_x){printf("ON\n");}

else if (!accel_x){printf("OFF\n");}

}

It works, but it seems that there is a lag. Forexample I hooked up a normal switch to the pin. On the terminal I get
0n
0n
....
I then press the switch
0n
0n
0n
....................... (Ons for about another second)
Off
Off

It is the same for the 0ff to On transition.
I thought maybe for some reason my ISR was consuming to much time, explaining the delay, and so I took all of my code out an left the default:

Code:

...

 else if (INTCONbits.RBIF && INTCONbits.RBIE)  /* Ints 3-6 (RB4, RB5, RB6, or RB7) changed. */

  {

    int_byte = PORTB;          /* You must read or write to PORTB */

    INTCONbits.RBIF = 0;     /*     and clear the interrupt flag         */

  }                                        /*     to clear the interrupt condition.  */

Thanks for anyhelp.

Re: Reading interupt pin as Standard IO

The delay may be the USART waiting for the transmit buffer to clear of "On"s before the "Off"s are being sent. Try setting a pin high/low and reading that, it is a much faster response time.

Re: Reading interupt pin as Standard IO

I second Mike's comment. I know the IFI loader's terminal window introduces a significant delay when there is continuous data coming in. Hyperterminal is much better.

I don't know how the Vex serial communication is implemented. It's likely that you're sending "on" and "off" messages faster than they can be transmitted, and that they're being buffered.

Re: Reading interupt pin as Standard IO

Quote:

Originally Posted by Alan Anderson

Exactly. Try printing the on/off messages only when the pin state changes.

Re: Reading interupt pin as Standard IO

Quote:

Originally Posted by GW (Greg) Ross

Exactly. Try printing the on/off messages only when the pin state changes.

Alright, I did that, and I am pretty sure that was the lag I was experiencing, so now I can poll the input and if it is different from the last input I print something to the screen.

Now I'm trying to do it with interrupts, and I have the code in the ISR as so:

Code:

        else if (INTCONbits.RBIF && INTCONbits.RBIE){  /* Ints 3-6 (RB4, RB5, RB6, or RB7) changed. */

                int_byte = PORTB;          /* You must read or write to PORTB */

                INTCONbits.RBIF = 0;     /*     and clear the interrupt flag */

                if(accel_x){

                        printf("High!n");

                }

                else if (accel_x ==0){

                        printf("LOW!n");

                }

        }

But I never get any output from the program, telling me that the interrupt is never... interrupting. Right?

[EDIT]-Stupid mistake... I never enabled interrupts by setting bit : INTCONbits.RBIE :-p

Re: Reading interupt pin as Standard IO

As a general rule, using printf in an interrupt service routine is a Bad Idea. The serial communication library routines might handle it without causing issues...or they might not.

ISRs should be reserved for things which take approximately no time to perform. Make a comparison, set a flag, store a value, maybe compute a delta or a sum. But try not to start something which will require waiting for something else to happen.

Re: Reading interupt pin as Standard IO

Quote:

Originally Posted by Alan Anderson

As a general rule, using printf in an interrupt service routine is a Bad Idea. The serial communication library routines might handle it without causing issues...or they might not.

I was just doing that to see when the ISR was running.
My actual code is

Code:

        else if (INTCONbits.RBIF && INTCONbits.RBIE){  /* Ints 3-6 (RB4, RB5, RB6, or RB7) changed. */

                int_byte = PORTB;          /* You must read or write to PORTB */

                INTCONbits.RBIF = 0;     /*     and clear the interrupt flag */

                

                if(accel_x){

                        //Here it measures the Low time

                        T1CONbits.TMR1ON = 0; // turn it off

                        accel_xTiltC=ReadTimer1();

                        WriteTimer1( 0x00 );

                        T1CONbits.TMR1ON = 1; // turn it on

                        Status = 2;

                }

                else if (accel_x ==0){

                        //This time it measures the High time

                        T1CONbits.TMR1ON = 0; // turn it off

                        accel_xTilt= ReadTimer1(); //capture timer value

                        WriteTimer1( 0x00 );

                        T1CONbits.TMR1ON = 1; // turn it on

                        Status = 1;

                }

        }

accel_xTilt is an unsigned integer, and since Timer1 is configured as a 16 bit timer, that should be suffice to hold any timer value right? But from 6ms - 4 ms I get negative values! I thought maybe for some reason it was wrapping around and doing something funny, so when I made it a long I got all zero values.
Does anyone have code that does frequency/duty cycle measurement?

Re: Reading interupt pin as Standard IO

Quote:

Originally Posted by intellec7

You probably had the right values in the accel_xTilt variable, but printf() has difficulty showing anything other than an int unless you cast things just right.

Re: Reading interupt pin as Standard IO

Quote:

Originally Posted by Alan Anderson

You probably had the right values in the accel_xTilt variable, but printf() has difficulty showing anything other than an int unless you cast things just right.

How did you know :-p. I had %d with an unsigned int... changed it to %u and voila. Thanks for your help.