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minus signs not showing up consistently in printf

 
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Harry Mueller



Joined: 17 Oct 2005
Posts: 116

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minus signs not showing up consistently in printf
PostPosted: Fri Apr 21, 2006 6:39 am     Reply with quote
In a debugging exercise I print out 3 variables. The calculations are all done correctly but two of the printed values, Accel_percent and Avg may or may not show a minus sign, it seems almost arbitrary. The value Acceleration , a value between +10,000 and -10,000 always shows the proper sign.

Here are the three printf statements:

Code:
    printf("\r\nAcceleration = %ld", accel_value);
    printf("\r\nAccel_percent = %4ld.%02ld", accel_value/100, accel_value%100);
    printf("\r\nAvg= %4ld.%02ld",running_av_accel/100, running_av_accel%100);

Any idea why this is happening and how it can be corrected?

Thanks, Harry
Ttelmah
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PostPosted: Fri Apr 21, 2006 8:23 am     Reply with quote
What compiler version?.
There was a bug that applied to a few versions, where if the 'carry' flag is set from one arithmetic operation, it incorrectly gets displayed as a 'sign', in printf...
If you do the arithmetic 'outside' the printf, it doesn't happen. Also consider that if you have a reasonably recent compiler, you could use %w instead of doing the splitting yourself. Also, look at ldiv.

Best Wishes
SherpaDoug



Joined: 07 Sep 2003
Posts: 1640
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PostPosted: Fri Apr 21, 2006 8:25 am     Reply with quote
Can you show us the declarations for these variables and the math that calculates them? I suspect somewhere you are using an unsigned type to hold a signed value.
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Harry Mueller



Joined: 17 Oct 2005
Posts: 116

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PostPosted: Fri Apr 21, 2006 9:40 am     Reply with quote
Ttelmah wrote:
What compiler version?.
There was a bug that applied to a few versions, where if the 'carry' flag is set from one arithmetic operation, it incorrectly gets displayed as a 'sign', in printf...
If you do the arithmetic 'outside' the printf, it doesn't happen. Also consider that if you have a reasonably recent compiler, you could use %w instead of doing the splitting yourself. Also, look at ldiv.

Best Wishes


My compiler version is 3.245. I will try using %w to see if that clears it up, however I would really like to know what is causing my problem just to learn more.

What is ldiv?

Thanks, Harry
Harry Mueller



Joined: 17 Oct 2005
Posts: 116

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PostPosted: Fri Apr 21, 2006 9:44 am     Reply with quote
SherpaDoug wrote:
Can you show us the declarations for these variables and the math that calculates them? I suspect somewhere you are using an unsigned type to hold a signed value.


I don't think I've done that but maybe I've missed something. Here is all my code....hope it's not too long to go through.
Code:
//This program computes acceleration and rate of change with an accelerometer
// and a gyro and uses these values to calculate torque for the DC motors.
// It uses an interrupt on port_b for both calculations.


#include <16F877.H>
#include <24256-1.c>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 20000000)
#use RS232(BAUD=38400,XMIT=PIN_C6,RCV=PIN_C7)//communication link with BotLoader

//raise this value as high as you can without overflowing the math
#define ADXL202_SCALING_FACTOR 100000

#define motor_fwd 0b00000011
#define motor_rev 0b11111100

//global vars...................................................................

int current_portb, delta_portb, count;
signed int16 running_av_accel, gyro_value;
unsigned int16 accel_period, accel_pulse, reading, adxl_ppg;
unsigned int16 accel_value_address, gyro_pulse, last_gyro_pulse;
signed int32 adxl_zerog;
static int8 index = 0, flag = 0;
static int last_portb;
static unsigned int16 accel_old_reading, gyro_old_reading;

//Initialization routines.......................................................

void motor_init()
 {
  int8 torque;
  int1 flag=0;
  //port_b_pullups(TRUE);                           // ????
  setup_timer_2(T2_DIV_BY_1,199, 1);                // 25 KHz
  setup_ccp1(CCP_PWM);                              // Configure CCP1 as a PWM
  setup_ccp2(CCP_PWM);                              // Configure CCP2 as a PWM
 }

void accelerometer_init(unsigned int32 zerog, long ppg)
{
   adxl_zerog=zerog;
   adxl_ppg=ppg;
   setup_timer_0 (RTCC_INTERNAL | RTCC_DIV_32);
   setup_timer_1 (T1_INTERNAL);
   enable_interrupts(INT_RTCC);
   enable_interrupts(INT_RB);
   enable_interrupts(GLOBAL);
}

//Interrupts service routines...................................................

#int_RTCC                                            // Output 1500 uS pulse
Gyro_input_isr()
{
 set_timer0(22);
 if (++count==12)
 count = 0;
 else
 {
 if(count<2)
 output_high(PIN_E2);
 else
 output_low(PIN_E2);
 }
}

#int_RB

void accel_gyro_isr(void)
{
reading = get_timer1();                              //Read Timer_1
current_portb = input_b();                           //Read value of PORT_B
delta_portb = (current_portb ^ last_portb) >> 4;     //Did PORT_B change?
last_portb = current_portb;                          //Remember PORT_B value
if ((delta_portb == 0x08) ||
    (delta_portb == 0x0c))                           //If PIN_B7 has changed
 {
  if (bit_test(current_portb, 7))                    //If PIN_B7 is high
  {
   accel_period = reading - accel_old_reading;       //Calculate period
   accel_old_reading = reading;
  }
  else
   accel_pulse = reading - accel_old_reading;         //Calculate duty
 }
  else if ((delta_portb == 0x02) ||
            (delta_portb == 0x06) ||
             (delta_portb == 0x0a) ||
              (delta_portb == 0x0e) ||
               (delta_portb == 0x0f))
   {
    if (bit_test(current_portb, 5))                  //If PIN_B5 is high
     gyro_old_reading = reading;                     // Record timer_1 reading
    else
     gyro_pulse = reading - gyro_old_reading;        //Calculate gyro_pulse
   }
 }

//Functions.....................................................................

// A(g) = (T1/T2 - 0.456) / 0.118
// 0g = 50% duty cycle
signed int16 accelerometer_read(void)
{
 signed int32 value;
 value = accel_pulse * ADXL202_SCALING_FACTOR;
 value = value / accel_period;
 value = value - adxl_zerog;
 value = (value  * 10000) / adxl_ppg;
 return(value);
}

signed int16 gyro_read(void)
{
 signed int32 value;
 value = (gyro_pulse / 5) - 1500;                // Covert ticks to change in uS
 return(value);
}

signed int16 running_average(signed int16 add_value)
 {
    static signed int16 vals[6], sum;
    signed int16 result;
    if ((index==0) && (flag == 0)) //discard phoney first value
    add_value = 0;
    if (flag==5)                 // continue once five values have been received
    {
     sum += add_value;
     sum -= vals[index];
     vals[index] = add_value;
     result = sum / 5;
     index = (index+1) % 5;
     flag = 5;
     return(result);
    }
    else                         //fill up the first 5 values and calculate sum
    {
     vals[index] = add_value;
     sum += add_value;
     result = sum / ++index;     
     if (index==5)
     index = 0;
     flag++;
     return(result);
    }
 }

motor_control()
{
 int16 K_accel = 1, K_gyro = 1;
 signed int16 torque = 0;
 torque = ((running_av_accel/100) * K_accel) +
           (gyro_value * K_gyro);
 //printf("\n\rMotor_control section.............................");
 //printf("\r\nrunning_av_accel = %ld ",running_av_accel/100);
 //printf("\r\ngyro_value = %ld ",gyro_value);
 //printf("\r\nTorque = %ld ",torque);
 i2c_start();
 i2c_write(0x40);
 if ((torque > 50) || (torque < (-50)))
 {
 if (torque > 0)
  i2c_write(0b00000011);
 else
  i2c_write(0b11111100);
 i2c_stop();
 set_pwm1_duty(4*abs(torque));            // calculated duty cycle on pin B2
 set_pwm2_duty(4*abs(torque));            // calculated duty cycle on pin B1
 }
  else;
}

//Main program..................................................................

main()
{
 accelerometer_init(45600,11750);         //calibrated values
 init_ext_eeprom();                       // initialize external EEPROM
 motor_init();                            // initialize motors
 {
  while (1)
   {
    signed int16 accel_value;
    accel_value = accelerometer_read();// "Value" varies from -10,000 to +10,000
    //write_ext_eeprom(accel_value_address, accel_value);
    running_av_accel = running_average(accel_value);
    gyro_value = gyro_read();
    motor_control();
    printf("\n\rMain section.................................................");
    printf("\r\nGyro rate of change = %ld%%",gyro_value);
    printf("\r\nAcceleration = %ld", accel_value);
    printf("\r\nAccel_percent = %4ld.%02ld", accel_value/100, accel_value%100);
    printf("\r\nAvg Acelleration = %4ld.%02ld",running_av_accel/100, running_av_accel%100);
    delay_ms(250);
   }
 }
}


Thanks, Harry
Harry Mueller



Joined: 17 Oct 2005
Posts: 116

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PostPosted: Fri Apr 21, 2006 12:28 pm     Reply with quote
Harry Mueller wrote:
Ttelmah wrote:
What compiler version?.
There was a bug that applied to a few versions, where if the 'carry' flag is set from one arithmetic operation, it incorrectly gets displayed as a 'sign', in printf...
If you do the arithmetic 'outside' the printf, it doesn't happen. Also consider that if you have a reasonably recent compiler, you could use %w instead of doing the splitting yourself. Also, look at ldiv.

Best Wishes


My compiler version is 3.245. I will try using %w to see if that clears it up, however I would really like to know what is causing my problem just to learn more.

What is ldiv?

Thanks, Harry


I used the %W format and it cleared the problem up. Thanks, Ttelmah, I didn't even know that existed.

Harry
Ttelmah
Guest
PostPosted: Fri Apr 21, 2006 2:30 pm     Reply with quote
The 'sign bug', was posted about a few weeks ago, with another poster performing arithmetic inside the printf, and getting similar behaviour. If I remember at the time, somebody posted the assembler listing being generated for the arithmetic. If the arithmetic is done outside the printf (put into a variable), it doesn't happen.
Glad %w at least solved the 'effect'. :-)

Best Wishes
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