/* RCC Set the Source for the System Clock.  */
void rcc_set_sysclk_source(uint32_t clk)
/* RCC Set the Source for the System Clock.  */
void rcc_set_sysclk_source(uint32_t clk)
{
	RCC_CFGR = (RCC_CFGR & ~RCC_CFGR_SW) |
			(clk << RCC_CFGR_SW_SHIFT);
}