How to generate random numbers in "C" with AVR Studio?

[avinash.kashyap]

...hi, i'm using AVR Studio/ GCC + WinAVR...and using function as n=rand()*6, trying to generate any random number between 0 to 5 but the problem is everytime my MCU gives me the same sequence of "random" numbers e.g. {6, 5, 3, 1, 4, 2 ...and it repeats}...so can someone help to generate real unpredictible random numbers?...

 

[alexan_e]

You can use this random number generator function,
I usually pass a value from a timer to it

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Code C - [expand]
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#define M 0x7FFFFFFF  // 2^31-1, the modulus used by the psuedo-random
 
long int prng(long int x) {  //random number generator; call with 1 <= x <=M-1
 x = (x >> 16) + ((x << 15) & M)  - (x >> 21) - ((x << 10) & M);
 if (x < 0) x += M;
 return x;
}

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Alex

 

[andre_luis]

The seed I already used was the A/D value due uC was measuring the main line voltage.
The reason is that it is really assincronous with uC timing.

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[uxmanz]

my idea....use timers....initiate one....take a number out...would be random every time u take it out.....timer running with 12mhz mips would change value every ((1/12)*10^-12) seconds!....no body is that quick

 

[andre_luis]

uxmanz,

If I understood correctly, what you posted don´t work.
Note that the built-in uC timer is colcked by same source than core.

It is necessary an external assincronous event to feed input of random funcion.
I performed something like what you said and generated everytime the same value.

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