Timing problem in C

Question

I dont have good experience on c... i just want to learn some of the practical scenarios to be implemented in c.... for example how can i implement the following in C code...

y=1 when x=1
y=0 when x!=1

the main thing is that....

output y changes when input x changes and has to maintain its state for 1 second if there is any change in the input within 1 sec it has to maintain its previous state.

please any one help me on this..and kindly help me how to approch for this type of logics.. please

@Matt: I'd say temporal logic, but that shows my theory background. — Charles Stewart
– Charles Stewart, Commented Dec 6, 2010 at 8:56
Woods (1989) Temporal logic case study gives an idea of how temporal logic is used to model these kinds of constraints, with the obligatory elevator running example. — Charles Stewart
– Charles Stewart, Commented Dec 6, 2010 at 8:59

ruslik · Accepted Answer · 2010-12-06 09:29:10Z

2

If you can afford busy waiting when x isn't changing, then

volatile int x;
int old_x, tmp = x;
while (1){
    y = ((old_x = tmp) == 1);
    Sleep(1000);
    while(old_x == (tmp = x));
}

if you have any event or interrupt when it's changed, it can be done without busy waiting.

edited Dec 6, 2010 at 9:29

answered Dec 6, 2010 at 8:54

ruslik

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3 Comments

Charles Stewart Over a year ago

The qner was also after general thoughts on coding these kinds of example.

ruslik Over a year ago

@Charles: it's almost all that C could do about VHDL's delay. Generic case should be tough..

lalli Over a year ago

+1 for using volatile. jack needs to develop on this. The part that's not mentioned in the question but is obvious is taking the input (which would require multithreading/multiprocessing).

Alex Reynolds · Accepted Answer · 2010-12-06 08:52:51Z

0

Once you figure out how you want to handle IO and timing, these are possibilities for the relevant test:

y = (x == 1 ? 1 : 0);

or:

if (x == 1) 
    y = 1;
else 
    y = 0;

or:

y = 0;
if (x == 1)
    y = 1;

answered Dec 6, 2010 at 8:52

Alex Reynolds

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1 Comment

Charles Stewart Over a year ago

This doesn't treat the IO constraints in the qn at all.

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