This is not strictly necessary, as
- at least for the Ricoh chip in the A3000 and A4000, as those chips' Y10
registers happily continue to count up from 0xA if manually incremented
past 0x9.
- the Amiga ROMs and "setclock" commands seem to interpret 0xA 0x? like
200?, etc.
However,
- the Amiga setclock writes the modulo 10 value into the chips
- the chip docs of both chips, including the Y2K information of their
manufacturers, only refer to the range 0-9
- the chips increment from 9 to 0
So we better conform to this, to avoid unpleasant surprises.
