rand()

[eunni]

Hi,

I want to use random number.

But, the same random number is generated each time it is run.

When I debug the code below, W change with the same pattern every time I debug.

What's the problem and is there any solution to make random number which is not depend on the order? 

/* USER CODE BEGIN 0 */

double uniform_rand(){

return (double)rand()/((double)RAND_MAX + 1);

}

/* USER CODE END 0 */

int main(void) {

/* USER CODE BEGIN 2 */

srand(time(NULL));

/* USER CODE END 2 */

while {

W = uniform_rand();

}

}

[mƎALLEm]

Hello,

What product you're using so you can use RNG peripheral instead of that "rand" library?

[eunni]

sorry but I can't understand what you're saying...

isn't it "rand" library?

srand(time(NULL));

[mƎALLEm]

rand() from stdlib.h

What MCU part number are you using?

[Tesla DeLorean]

Need to seed it better.

Is there a clock or anything behind time() ? There'd need to be some association with the RTC and it would need to be running.

[eunni]

Yes I use rand() function from stdlib.h

I'm using 2 kinds of board for i2c.

One is U575ZI-Q for master and the other is L432KC for slave.

[eunni]

I didn't use anything according to the clock.

Is there any recommandation to make better seed?

srand(time(NULL)); <----------- I think it change seed every single second

[Tesla DeLorean]

That supposes time() is working and there's anything making it tick.

In embedded you'd actually need to facilitate this.

You should confirm that it is working as you imagine.

[mƎALLEm · Accepted solution]

---

I'm using 2 kinds of board for i2c.

One is U575ZI-Q for master and the other is L432KC for slave.

---

Hello,

The two devices feature RNG (random number generator) as shown in their respective DS:

You can inspire from one of the examples of RNG. Example:

https://github.com/STMicroelectronics/STM32CubeL4/tree/master/Projects/NUCLEO-L432KC/Examples/RNG/RNG_MultiRNG