// setup PLL from external crystal (PR0), F_crystalu=16MHz, F_CPU=16*8/4 = 32MHz
void clock_init(void){
	CCP=CCP_IOREG_gc; // unlock writing to CLK.PSCTRL
	CLK.PSCTRL = CLK_PSADIV_8_gc; // Set up prescalers
	OSC.XOSCCTRL = OSC_FRQRANGE_12TO16_gc | OSC_XOSCSEL_XTAL_16KCLK_gc; // vybrat zdroj pro XOSC (krystal) a parametry oscilátoru
	OSC.CTRL = OSC_XOSCEN_bm; // start external clock
	while (!(OSC.STATUS & OSC_XOSCRDY_bm)){};	// wait until external clock is stabilized
	OSC.PLLCTRL = OSC_PLLSRC_XOSC_gc | 8; // setup PLL source (external clock), PLL_FAC = 30 (multiply clock 30x)
	OSC.CTRL |= OSC_PLLEN_bm; // enable PLL
	while (!(OSC.STATUS & OSC_PLLRDY_bm)){};	// wait until PLL is stabilized
	
	CCP=CCP_IOREG_gc; // unlock writing to CLK_CTRL
	CLK.CTRL = CLK_SCLKSEL_PLL_gc; // select PLL as system clock
}