I have an STM32G071 running FreeRTOS CMSIS v2 compiled with STM32CubeIDE. In one of the threads I want to generate a pseudo-random number. (I don't need anything sophisticated and the STM32G071 doesn't have an RNG anyway; pseudo random is absolutely fine for my purposes).
The code snippets show calls to srandom() and random() but the results were identical with srand() and rand() too.
If I call rand() or random() from anywhere in main() before I call osKernelStart(), all is well:
int main(void)
{
HAL_Init();
SystemClock_Config();
osKernelInitialize(); // Init scheduler
/* random number test - this works */
uint32_t x = 0;
srandom(12345);
x = random(); // returns a random number
osKernelStart(); // Start scheduler
/* We should never get here as control is now taken by the scheduler */
/* Infinite loop */
while (1)
{
}
}
But if I call rand() or random() anywhere in a thread, it always returns 0 (even if I call srand() or srandom() with a seed immediately beforehand). Clearly, I wouldn't call srandom() each time, I'm just showing that it isn't making any difference here:
void my_thread (void *argument)
{
UNUSED (argument);
/* random number test - this fails */
uint32_t x;
srandom(12335);
x = random(); // always returns 0 for any seed
/* Infinite loop */
for (;;)
{
osDelay(10;)
}
}
It doesn't make any difference whether the call to rand() or random() in the thread is before the infinite while loop or during it, same result.
I know that srand() and srandom() aren't re-entrant but if I'm only calling them from one point in one thread it shouldn't matter as the thread itself isn't re-entrant.
Does anyone know what the problem is?
