I maybe will be able to use the same processor to run another planned railroad project.
I'll use an interrupt so I will not be constantly polling the registers for a change,
By logging the nudge(s) required, the next time that location is moved to, the nudges will occur automatically. Count would be kept in EPROM, so information would not be lost when powering down.
it makes sense to increase the resolution right from the beginning
I wanted to be able to anticipate approaching the final destination, and start to slow the drive motor speed down in steps before reaching the destination.
There's at least one shield that already does this, although I suspect you'd rather cook up your own home-grown design: http://docs.macetech.com/doku.php/centipede_shield