BCD Subtraction intrinsic?

[Mac 67]

Hi guys. A couple questions, please?

 

(1) Anyone know if there's a reciprocal for the _bcd_add_short() intrinsic function that I can use to decrement packed BCD variables for a countdown timer routine?

 

(2) If there isn't a BCD subtract instrinsic, is there a good way to do decrement a packed BCD number in C, without resorting to in-line assembly code?

 

TIA! Regards, Mike

 

   #define timer_running (hh|mm|ss)

   /*
   *  countdown timer, hh:mm:ss (1 second intervals)
   */
   if(timer_running)                     //
   { if(ss != 0x00)                      // if seconds not 0x00
     { asm("  clrc              ");      // decrement seconds
       asm("  dadd.b  #0x99,&ss ");      // (packed BCD)
     } else                              // else, seconds == 0x00 so
     { ss = 0x59;                        // reset seconds to 0x59 and
       if(mm != 0x00)                    // if minutes not 0x00
       { asm("  clrc              ");    // decrement minutes
         asm("  dadd.b  #0x99,&mm ");    // (packed BCD)
       } else                            // else, minutes == 0x00 so
       { mm = 0x59;                      // reset minutes to 0x59 and
         asm("  clrc              ");    // decrment hours
         asm("  dadd.b  #0x99,&hh ");    // (packed BCD)
       }                                 // 
     }                                   //
     if(!timer_running)                  // if timer has timed-out
       P1OUT ^= relay_pin_mask;          // turn relay output off
   }                                     //

[RobG 1,892]

How about

 

_bcd_add_short(-1)

 

Never mind, that function takes unsigned

[Mac 67]

How about

_bcd_add_short(-1)

 

Excellent! Thank you! I really should have thought of that (argh!)...

[RobG 1,892]

Never mind, that function takes unsigned

 

How about overflowing your destination variable?

a = _bcd_add_short(a, 0x9999);

[Mac 67]

I spoke too soon (grin). I'm trying some variations right now...

[RobG 1,892]

a = _bcd_add_short(a, 0x9999);

Works as expected, 0x9999 is -1, 0x9998 is -2, etc.

[Mac 67]

That should do it...

 

   /*
   *  countdown timer, hh:mm:ss (1 second intervals)
   */
   if(timer_running)                     //
   { if(ss)                              // if seconds > 0x00
     { ss = _bcd_add_short(ss,0x99);     // decrement seconds
     } 
     else                                // else, seconds == 0x00 so
     { ss = 0x59;                        // reset seconds to 0x59 and
       if(mm)                            // if minutes > 0x00
       { mm = _bcd_add_short(mm,0x99);   // decrement minutes
       } 
       else                              // else, minutes == 0x00 so
       { mm = 0x59;                      // reset minutes to 0x59 and
         hh = _bcd_add_short(hh,0x99);   // decrement hours
       }                                 //
     }                                   //
     if(!timer_running)                  // if timer has timed-out
       P1OUT ^= relay_pin_mask;          // turn relay output off
   }                                     //