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Calculation with fixed numbers.

 
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bschriek



Joined: 18 Dec 2007
Posts: 82

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Calculation with fixed numbers.
PostPosted: Mon Apr 14, 2025 1:40 am     Reply with quote
PCW Compiler, IDE 5.118, 16F18124

I use the "NCO_FIXED_DUTY_MODE" and "CWG_MODE_HALF_BRIDGE" to control a half-bridge. This works fine!
To set the frequency at 55kHz I need to fill the NCO varible with 7256d.
Code:
Freq = 7256;                // int16
set_nco_inc_value(Freq);    // = 55kHz

But for better understanding I like to use a simple calculation/description.
Code:
Freq = (55000 / 7.58);         // Here I can see immediately the frequency is 55kHz. 
set_nco_inc_value(Freq);       // = 55kHz

I also have a simple while loop as you can see underneath:
Code:
Freq = (75000 / 7.58);         // Here I can see immediately the frequency is 75kHz.
while (Freq > (55000/7.58))    // And here it's 55kHz
      {
      ......... code
      set_nco_inc_value(Freq);
      delay_us(50);       
      }

I thought the compiler does this calculation and converts to a constant but it's not.
When I open the .LST file this calculation is fully performed in the program and uses a lot of memory and time.
Probably a silly question but any help is welcome.
temtronic



Joined: 01 Jul 2010
Posts: 9457
Location: Greensville,Ontario

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PostPosted: Mon Apr 14, 2025 4:47 am     Reply with quote
my gut is saying that 'freq=..' will be calculated during compile BUT the 'while(........) 'test' will be calculated every time ??
bschriek



Joined: 18 Dec 2007
Posts: 82

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PostPosted: Mon Apr 14, 2025 5:53 am     Reply with quote
Yes, you are right.
Problem is reduced to 50%. Laughing
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