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Strange ">=" problem

 
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LukeD
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Strange ">=" problem
PostPosted: Sat Jan 10, 2009 11:56 am     Reply with quote
Hello!

I'm working on a simple fading example, to test PWM... but I noticed a strange problem in the fade_down() sub.

The for loop never ends:

Code:
for(step = max_duty; step >= 0; step--) {


The only way I can stop it at the correct value is change to:

Code:
for(step = max_duty; step != -1L; step--) {


Maybe it's a stupid mistake but I can't find it...
Thanks!


Code:

#include "main.h"
#include <string.h>

#define PR2 20
#define BUFFER_SIZE 10
#define CR 0x0d
#define LF 0x0a
#define STEP_DELAY 30

char help_cmd[5] = "?";
char fadeup_cmd[10] = "FADEUP";
char fadedown_cmd[10] = "FADEDOWN";
char fadex_cmd[10] = "FADEX";

long max_duty;
char input_buffer[BUFFER_SIZE];
int input_index;
int1 input_ok;
long step;

#INT_RDA
void rs232_isr(void) {

   char temp;
   temp = getc();

   if (temp == CR) {
      input_buffer[input_index] = '\0';     
      input_ok = true;
      printf("\r\n");
      return;
   }

   if (temp == LF) return;

   putc(temp);
   input_buffer[input_index] = toupper(temp);
   
   if (input_index >= (BUFFER_SIZE - 1)) input_index = 0;
   else input_index++;
}


void fade_up() {
 
   setup_timer_2(T2_DIV_BY_1, PR2, 1);
   set_pwm1_duty(0);
   printf("  Start fading up...\r\n");
   
   setup_ccp1(CCP_PWM);
   for(step = 0; step <= max_duty; step++) {
      printf("%Ld\t", step);
      set_pwm1_duty(step);
      delay_ms(STEP_DELAY);
   }
   
   printf("  ...done!\r\n");
}


void fade_down() {

   setup_timer_2(T2_DIV_BY_1, PR2, 1);
   set_pwm1_duty(max_duty);
   printf("  Start fading down...\r\n");
   
   setup_ccp1(CCP_PWM);
   for(step = max_duty; step >= 0; step--) {
      printf("%Ld\t", step);
      set_pwm1_duty(step);
      delay_ms(STEP_DELAY);
   }
   
   printf("  ...done!\r\n");
}


void usage() {

   printf("  Available commands:\r\n");
   printf("  FADEUP - start fading up\r\n");
   printf("  FADEDOWN - start fading down\r\n");
   printf("  FADEX - start cross fading\r\n");
}


void decode_command() {

   if (strcmp(input_buffer, fadeup_cmd)==0)
      fade_up();
   else if (strcmp(input_buffer, fadedown_cmd)==0)
      fade_down();
   else if (strcmp(input_buffer, fadex_cmd)==0) {
      fade_up();
      delay_ms(STEP_DELAY);
      fade_down();
   }
   else if (strcmp(input_buffer, help_cmd)==0)
      usage();
   else printf("  Unknown command: %s\r\n", input_buffer);
}


void main() {
   
   setup_ccp1(CCP_OFF);
   max_duty = 4 * (PR2 + 1);

   input_ok = False;
   input_index = 0;
   
   disable_interrupts(GLOBAL);
   enable_interrupts(INT_RDA);
   enable_interrupts(GLOBAL);
   printf("> ");

   while(1) {

      if(input_ok) {
     
         disable_interrupts(GLOBAL);
         input_ok = False;
         decode_command();
         
         printf("> ");
         input_index = 0;
         enable_interrupts(GLOBAL);
      }
   }
}
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sat Jan 10, 2009 12:55 pm     Reply with quote
In CCS, all integer data types are unsigned by default. An unsigned
integer can never be less than 0. To make 'step' into a signed value,
you need to declare like this:
Quote:
signed long step;
LukeD
Guest
PostPosted: Sun Jan 11, 2009 2:03 pm     Reply with quote
Embarassed thanks and sorry for the dumb question
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