33.4.8.2 Double Sample Conversion
Double sampling is enabled by setting the DSEN bit. When this bit is set, two conversions are required before the
            module calculates the threshold error. Each conversion must be triggered separately when
            CONT = 0, but will repeat automatically
            form a single trigger when CONT = 1. The first conversion will set the
                MATH bit and update the ADACC
            register, but will not calculate ADERR or trigger ADTIF. When the second
            conversion completes, the first value is transferred to ADPREV
            (depending on the setting of PSIS) and the value of the second conversion is placed into ADRES. Only
            upon the completion of the second conversion is ADERR calculated and ADTIF triggered (depending on the value
            of CALC).
