Get_Gyro_Angle() overflows beyond about -20000 deci-decgrees?

[gnormhurst]

I'm trying to make an approximate lap counter by dividing the accumulated gyro angle by 360 (or 3600, since I'm working in decidegrees).

It works up to 5 laps, then the gyro value seems to wrap around to the positive side and start decreasing. I'm using long ints for the calculations. Here is a simplified version of the code....

  long int gyroAngle;
  unsigned int  numLaps = 0;

  gyroAngle = Get_Gyro_Angle();
  if ( gyroAngle < 0L ) gyroAngle = -gyroAngle;  //absolute value.
  
  numLaps = (unsigned int) ( (gyroAngle) / (long int)3600);
  printf( "gyro: %5ld LAPS = %2d\r\n", (gyroAngle), (int)numLaps );


//   etc.....

I looked at the gyro.c code briefly. Get_Gyro_Angle() (below) returns a long int, but there's a bunch of #defined constants, not all of which sport the decorative "L" at the end. (BTW, does "L" make a literal into a short int (16) or a long int (32)? I checked the compiler manual and didn't see it defined.)

long Get_Gyro_Angle(void)
{
	// Return the calculated gyro angle to the caller.
	return(((gyro_angle * GYRO_SENSITIVITY * 5L) / (ADC_RANGE * ADC_UPDATE_RATE)) * GYRO_CAL_FACTOR);
}

Why can't I get big values out of Get_Gyro_Angle()? e.g. 6 laps = 6 * -3600 = -21600.

[Joe Ross]

Originally Posted by gnormhurst

I'm trying to make an approximate lap counter by dividing the accumulated gyro angle by 360 (or 3600, since I'm working in decidegrees).

It works up to 5 laps, then the gyro value seems to wrap around to the positive side and start decreasing. I'm using long ints for the calculations. Here is a simplified version of the code....

  long int gyroAngle;
  unsigned int  numLaps = 0;

  gyroAngle = Get_Gyro_Angle();
  if ( gyroAngle < 0L ) gyroAngle = -gyroAngle;  //absolute value.
  
  numLaps = (unsigned int) ( (gyroAngle) / (long int)3600);
  printf( "gyro: %5ld LAPS = %2d\r\n", (gyroAngle), (int)numLaps );


//   etc.....

I looked at the gyro.c code briefly. Get_Gyro_Angle() (below) returns a long int, but there's a bunch of #defined constants, not all of which sport the decorative "L" at the end. (BTW, does "L" make a literal into a short int (16) or a long int (32)? I checked the compiler manual and didn't see it defined.)

long Get_Gyro_Angle(void)
{
	// Return the calculated gyro angle to the caller.
	return(((gyro_angle * GYRO_SENSITIVITY * 5L) / (ADC_RANGE * ADC_UPDATE_RATE)) * GYRO_CAL_FACTOR);
}

Why can't I get big values out of Get_Gyro_Angle()? e.g. 6 laps = 6 * -3600 = -21600.

gyro_angle * GYRO_SENSITIVITY * 5L is overflowing a long. Kevin's latest gyro code gives a little more headroom by rearranging the order operations are done to not overflow as early.

[gnormhurst]

Okay, I'll check out Kevin's newer code....

BTW, for my current code I dereferenced the macros and got

long Get_Gyro_Angle(void)
{
	// Return the calculated gyro angle to the caller.
	return(((gyro_angle * GYRO_SENSITIVITY * 5L) / (ADC_RANGE * ADC_UPDATE_RATE)) * GYRO_CAL_FACTOR);
        // translates to:
	//return(((gyro_angle * 800L * 5L) / (1024L * ADC_SAMPLE_RATE/(ADC_SAMPLES_PER_UPDATE * NUM_ADC_CHANNELS))) * 958/1000);
        // which translates to ...
	//return(((gyro_angle * 800L * 5L) / (1024L * 200/(4 * 1))) * 958/1000);

	
}

I guess I could make my own Get_Gyro_Angle_Low_Resolution() that doesn't use such a large value for GYRO_SENSITIVITY.

[gnormhurst]

I've seen the gyro.c,h code in the new 3.0 compatible code. I am using 2.4. Can I just drop the gyro.c,h files into my code and expect everything to be fine? Or are there 3.0/2.4 issues?