/* RCC Set the USB Prescale Factor. 
The prescale factor can be set to 1 (no prescale) for use when the PLL clock is 48MHz, or 1.5 to generate the 48MHz USB clock from a 64MHz PLL clock. */
void rcc_set_usbpre(uint32_t usbpre)
/* RCC Set the USB Prescale Factor. 
The prescale factor can be set to 1 (no prescale) for use when the PLL clock is 48MHz, or 1.5 to generate the 48MHz USB clock from a 64MHz PLL clock. */
void rcc_set_usbpre(uint32_t usbpre)
{
	if (usbpre) {
		RCC_CFGR |= RCC_CFGR_USBPRE;
	} else {
		RCC_CFGR &= ~RCC_CFGR_USBPRE;
	}
}