C Problem in VI

[dhanna]

first formula node of C there, giving me maxAch (61) of 1666667, and hence, distorting what i want with the rest of the VI, when i want to be 2000000? despise C/C++ etc with a passion!lol

In case VI doesnt run, i've attached pics of the probes and data etc. to show

[nathand]

Sorry, no idea what you're asking here. Are you asking if your formula is correct, or are you saying that LabVIEW is miscalculating the result, or something else?

[dhanna]

as in the code within the formula node, its producing an output of 1.67x10^6 but i want 2x10^6, i suppose a C forum may be a better place to ask

[johnsold]

Please set the controls to values which illustrate your problem and make those values default before saving and posting the VI. 

When I set the controls to:

maxFFin = 2E+6

sCLKin = 60000000

ffin = 200000

bit = 18

taq = 3E-7

spec = 200000

The results are:

sCLKout = 60000000

maxAch = 200000

ffOut = 200000

If you do not like the formula node syntax, why use it? There does not apper to be anything in there which could not be implemented in a straightforward way with LV primitives.

Lynn

[Zwired1]

Your VI is driven by the controls below but the values you are using when you get your unexpected result did not get posted with your VI/message.  Please let us know. 

Your C code is not particular complex or long and you're not doing anything exotic so this forum is a reasonable choice.

A little bit of context may also help here, too.  What is it your code is used for? 

[Dennis_Knutson]

Where did you copy it from? Ask there.

[johnsold]

One of the itermediate calculations in the left formula node may have roundoff problems. When I duplicated the calculation with LV primitives, I get different results when using single and double precision.

inte = sCLKout*((bit/sCLKout)+taq)

sCLKout = 6E7

bit = 17

taq = 3E-7

inte (DBL) = 35.000000000000007100

inte (SGL) = 35.000000000000000000

The ceiling operation gives different results, 36 and 35, respectively.

Reconfiguring the calculation as inte = bit + taq*sCLKout has fewer operations and may not be as sensitive to round off errors.

In the while loop the lower shift register produces a result identical to the iteration count. Just wire the "i" terminal to the output.

Lynn

[Zwired1]

Wow. Kudo'd that.

[dhanna]

whenever i lose the line 'inte= etc' i get the output of 2x10^6 with the values of maxFFin, sCLKin, ffin , bit ,taq ,spec . probably just an instance of this working as opposed a long term solution.

changing inte to inte = bit + taq*sCLKout; stil gives me 1.67x10^6 output 

[dhanna]

with the inputs coming in still an output of 1.67x10^6 being produced, seen by the red arrow