hpdrive changes: dac holdoff

Hi Dave,

I predict exposing a dac holdoff release function is going to cause
difficulties.  Every "nec7210 compatible" chip handles dac
holdoff/release slightly differently and it was a nightmare trying to
reach some lowest common denominator in the nec7210 driver where no
bytes would get thrown away and the holdoff would reliably be
released.

Is there anywhere I could get info on why dac holdoff release control
is required by hpdrive emulation?  Also, why does it care about
secondary addressing state?

-- 
Frank