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Ideas for packing in more code into program memory

 
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arunb



Joined: 08 Sep 2003
Posts: 492
Location: India

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Ideas for packing in more code into program memory
PostPosted: Thu May 04, 2006 8:18 am     Reply with quote
Hi,

Is the modular approach the best method for increasing ROM space ??

I find that calling a function a number of times reduces ROM space..
Also how does breaking up a large function into smaller ones improves matters ??

thanks
arunb
Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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PostPosted: Thu May 04, 2006 8:42 am     Reply with quote
Compare the assembled code for the following.
Code:
   for (x=0;x<5;x++)
   {  x=y;
   }
   
   x=0;
   x=1;
   x=2;
   x=3;
   x=4;
   
   for (x=0;x<10;x++)
   {  x=y;
   }
   
   x=0;
   x=1;
   x=2;
   x=3;
   x=4;
   x=5;
   x=6;
   x=7;
   x=8;
   x=9;


Code:
....................    Int8 x,y;
....................
....................    for (x=0;x<5;x++)
0680:  CLRF   4B
0682:  MOVF   4B,W
0684:  SUBLW  04
0686:  BNC   0690
....................    {  x=y;
0688:  MOVFF  4C,4B
....................    }
068C:  INCF   4B,F
068E:  BRA    0682
....................
....................    x=0;
0690:  CLRF   4B
....................    x=1;
0692:  MOVLW  01
0694:  MOVWF  4B
....................    x=2;
0696:  MOVLW  02
0698:  MOVWF  4B
....................    x=3;
069A:  MOVLW  03
069C:  MOVWF  4B
....................    x=4;
069E:  MOVLW  04
06A0:  MOVWF  4B
....................
....................    for (x=0;x<10;x++)
06A2:  CLRF   4B
06A4:  MOVF   4B,W
06A6:  SUBLW  09
06A8:  BNC   06B2
....................    {  x=y;
06AA:  MOVFF  4C,4B
....................    }
06AE:  INCF   4B,F
06B0:  BRA    06A4
....................
....................    x=0;
06B2:  CLRF   4B
....................    x=1;
06B4:  MOVLW  01
06B6:  MOVWF  4B
....................    x=2;
06B8:  MOVLW  02
06BA:  MOVWF  4B
....................    x=3;
06BC:  MOVLW  03
06BE:  MOVWF  4B
....................    x=4;
06C0:  MOVLW  04
06C2:  MOVWF  4B
....................    x=5;
06C4:  MOVLW  05
06C6:  MOVWF  4B
....................    x=6;
06C8:  MOVLW  06
06CA:  MOVWF  4B
....................    x=7;
06CC:  MOVLW  07
06CE:  MOVWF  4B
....................    x=8;
06D0:  MOVLW  08
06D2:  MOVWF  4B
....................    x=9;
06D4:  MOVLW  09
06D6:  MOVWF  4B


If you start looking at the assembled code from the C code you write you will get a feel for the way to make code run fast ,use less space or easy to read. It is a big advantage to know how the C you write will assemble.
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