C codes for decoding RC5 signals using PIC microcontoller

/*--------------------------------------------------------------------
 
  Filename    : rc_decoder.c 
  
----------------------------------------------------------------------

  CHANGE HISTORY

  Issue   Modifier  Date      Change Description
  1.0     RW        29/08/07  First Issue
    
--------------------------------------------------------------------*/

#include <your include file?>

/*--- Macros ---*/

#define RC_PIN PORTDbits.RD8

#define RC_ADDRESS      16U
#define RC_VOLUME_UP    16U
#define RC_VOLUME_DOWN  17U
#define RC_INPUT_UP     51U   
#define RC_INPUT_DOWN   52U      
#define RC_STATUS       53U   
#define RC_GAIN         54U   
#define RC_PHASE        55U   
#define RC_MUTE         13U   
#define RC_STANDBY      12U       

/*--- RC code structure ---*/

typedef struct
  {
  Bool toggle;
  uint8_t address;
  uint8_t command;
  }RC_CODE;

volatile RC_CODE RC_CODEbits;
volatile RC_EVENT RC_EVENTbits;

/*--- Local function prototype ---*/

static void init_timer_6(void);
static Bool rc_decoder(void);
static Bool wait_while_low(void);
static Bool wait_while_high(void);

/*--- initialise rc decoder interrupt ---*/

void init_rc_decoder(void)
  {
  IPC5bits.INT1IP = 2;      /* Low Priority */ 
  INTCON2bits.INT1EP = 1;   /* Negative edge interrupt */
  init_timer_6();
  RC_EVENTbits.event = False;
  IFS1bits.INT1IF = 0;
  IEC1bits.INT1IE = 1;
  TRISDbits.TRISD8 = 1;
  } 

/*--- Initialise Timer 6 (Used as RC timer) ---*/

static void init_timer_6(void)
  {
  T6CON = 0;  
  IPC11bits.T6IP = 1;    
  T6CONbits.TCKPS = 3;  /* Prescale 1:256 */ 
  PR6 = 720;            /* ~5mS Time out */      
  IFS2bits.T6IF = 0;
  IEC2bits.T6IE = 0;    /* Not using interrupt */
  T6CONbits.TON = 1;
  }

/*--- Rc interrupt ---*/

void __attribute__((__interrupt__, no_auto_psv)) _INT1Interrupt(void)
  {
  IEC1bits.INT1IE = 0; 
  
  if(rc_decoder()){
    execute_rc_event(); /* resolve RC event */
    }
    
  IFS1bits.INT1IF = 0;    
  IEC1bits.INT1IE = 1;
  }

/*--- RC decoder function ---*/

static Bool rc_decoder(void)
  {
  uint16_t bit_counter, bit_time, test_time, limit, rc_code;

  TMR6 = 0; 
  
  if(!wait_while_low()){
    return False;
    }

  if(!wait_while_high()){        
    return False;
    }

  bit_time = TMR6;                /* Calibrate bit time */
  TMR6 = 0; 
 
  test_time = (bit_time / 4) * 3; /* 3/4 bit time */
  limit = (bit_time / 4) * 5;     /* Out of limits */
  
  for(bit_counter = 0; bit_counter < 12; bit_counter++)
    {
    while(TMR6 < test_time){
      continue;
      }

    if(RC_PIN == 1)
      {
      if(!wait_while_high()){        
        return False;
        }

      bit_time = TMR6;
      TMR6 = 0;

      if(bit_time < limit){
        rc_code <<= 1;
        rc_code |= 1;
       }
      }
    else if(RC_PIN == 0)
      {
      if(!wait_while_low()){        
        return False;
        }

      bit_time = TMR6;
      TMR6 = 0;

      if(bit_time < limit){
        rc_code <<= 1;
        rc_code &= 0xfffe;
        }
      }
    }
  
  RC_CODEbits.address = (rc_code >> 6) & 0x001f;
  RC_CODEbits.command = rc_code & 0x003f;
  RC_CODEbits.toggle = (rc_code >> 11) & 0x0001; 

  return True;
  }

/*--- Wait while line is low ---*/

static Bool wait_while_low(void)
  {
  Bool result = True;

  IFS2bits.T6IF = 0;

  while(RC_PIN == 0){
    if(IFS2bits.T6IF == 1){  /* Timeout */
      result = False;
      break;
      }
    }
  return result;
  }

/*--- Wait while line is high ---*/

static Bool wait_while_high(void)
  {
  Bool result = True;

  IFS2bits.T6IF = 0;

  while(RC_PIN == 1){
    if(IFS2bits.T6IF == 1){  /* Timeout */
      result = False;
      break;
      }
    }
  return result;
  }

/*--- Execute rc event ---*/

void execute_rc_event(void)
  {
  //To Do

  }

/*--- End of File ---*/

/*--------------------------------------------------------------------
  File Name     : PosixTypes.h 
  Description   : ISO (Posix) typedef file for pic
                : Misra Rule 6.3 (advisory)                      

  Revision      : 1.0 
  Date          : 21/08/05 
  
----------------------------------------------------------------------*/  

#ifndef TYPES_H
#define TYPES_H
            
/*--- Standard type definitions. ---*/

/* Plain char, only to be used for the storage and use of character values. Misra Rule 6.1 (Required) */

typedef unsigned char   uint8_t;    /* unsigned 8 bit type definition */
typedef signed char     int8_t;     /* signed 8 bit type definition */
typedef unsigned int    uint16_t;   /* unsigned 16 bit type definition */
typedef signed int      int16_t;    /* signed 16 bit type definition */
typedef unsigned long   uint32_t;   /* unsigned 32 bit type definition */
typedef signed long     int32_t;    /* signed 32 bit type definition */
typedef unsigned char   Bool;       /* Bool type definition */

/*--- Standard constant definition. ---*/

#define False ((Bool)0x00U)
#define True  ((Bool)0x01U)

/*--- End of file. ---*/

#endif