Servo Jumpy with DT Interrupt

[Jerson]

Hi Joe

Your observation seems to confirm what I'm saying. All software timed processes like Serout or Pulsout are affected by interrupts biting into their timing. I have had this experience before with regards to Serin and Serout. HPWM is a hardware timed process as is HSERIN or HSEROUT which work with devices that have the relevant hardware built in. Unfortunately, there is no HPULSIN or HPULSOUT in PbP.

I haven't used servos at all

[Acetronics2]

Hi, Dick

In an effort to increase the accuracy of timekeeping

Could you just explain what you want to do ???

if you want your servo to work properly ...

OR you disable interrupts while the PULSOUT Command ...

OR you place the PULSOUT Command into the interrupt stubb ...

BUT you must not interrupt the Pulsout command.

So, I do not think you can reach your goal, if you keep a RTC timer interrupt period that is lower than the PULSOUT max duration ...

Now ... I do not see any other way using pure PBP and Elapsed Timer with a 16F690 ... as it needs Timer 1.

Alain

[Mike, K8LH]

Have you considered using the PWM module? Many people don't realize you can run the PWM module at very low frequencies by using a software "helper" ISR (interrupt service routine) to link together several much smaller/faster PWM period "frames" to form a much longer/slower overall period.

This method provides many of the advantages of the PWM module (zero jitter, interrupt tolerant, very high resolution pulse width, etc.) at the cost of using a small low overhead ISR software "helper". You can also use the 1-msec interrupt interval as a basis for timer operations.

Perhaps one of the PBP gurus can convert, test, and qualify this code for you?

Happy Holidays!

Mike, K8LH

  //  setup a 1000 usec PWM period with PR2 = 249 and prescaler
  //  16:1 (16 MHz clock) or 4:1 (4 MHz clock) and then link 20
  //  of these 1000 usec PWM "frames" together to form the much
  //  longer 20-ms servo period (1-usec pulse width resolution)

  int servo = 1500;            // 0..20000 in 1 usec steps
  int frame = 1;               // frame number 1..20

  void interrupt()             //
  { int width;                 // work variable
    pir1.TMR2IF = 0;           // clear Timer 2 interrupt flag
    frame--;                   //
    if (frame == 0)            // if end of the 20 msec period
    { frame = 20;              // reset for new 20 msec period
      width = servo;           // reset 'width' work variable
    }
    if ((width > 1000)         // if width > 1000 usecs
    { ccpr1l = 250;            // do a 100% duty cycle frame
      ccp1con.CCP1Y = 0;       //
      ccp1con.CCP1X = 0;       //
      width -= 1000;           // subtract 1000 usecs
    }
    else                       // else do a 0..1000 usec frame
    { ccpr1l = (width >> 2);   // 0..250 (0..1000 usecs)
      ccp1con.CCP1Y = (width & 1);
      ccp1con.CCP1X = (width & 2);
      width = 0;               // force remaining frames to 0%
    }
  }