Demonstrations for cmp0 operation.

example code：
	P select XP42(PD9)
	N select DAC value
	OUT select PC8
	
	PB11 toggle putin P(cmp0)（XP42）
	read OUT(cmp0) state and print
	get edge state in cmp0 interrupt and print
		
	
1. DAC voltage calculate：
	FCLK：200M。
	
	VDD: IC power voltage
	DAC voltage calculate：Vdacx = VDD* DACx_CODE/4096
							   = 3.3V * 1000/4096
							   = 0.8V
				OR
							Vdacx = VDD* DACx_CODE/4096
								   = 5V * 1000/4096
								   = 1.22V
2、DAC value set 1000.


