Lpc2000

At 07:58 PM 4/8/05 +0000, ed_hage wrote:
>I have a simple interrupt-function for the PWM which reads the duty
>cycle variable and then sets the DC. This does not work. In the
>example beneath MR6 does give a good duty cycle (but is fixed!! so no
>pracitcal use), and when I use the float DC1 (as in MR4) it does not
>work. This is probably a problem which I may encounter more using
>floats etc. What is the best known method to deal with this? (I am
>newby in programming embedded ... as you might have guessed.


Two methods are available
         - The complex way is to save the floating point state, init a new 
floating point state, do your calculations and restore the floating point 
state.  Even if it's possible it's messy and take a while.
         - The more usual method is to use fractional or fixed point 
arithmetic (slight variations on a theme).  In your case


>   PWM_MR6 = 0.8*PWM_MR0;


Becomes

         PWM_MR6 = (8 * PWM_MR0) /10;

The brackets are important and you need to make sure the intermediate 
multiply cannot overflow (by working in the next size integer type if 
necessary.

Robert

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