Preferred OS, processor family for running embedded Ada?

["Mike Silva" <snarflemike@yahoo.com>]

First a bit of background.  I'm a longtime embedded programmer and a
dabbler in Ada (I'd use it more if I could get paid for it).  Now I'd
like to play around with Ada on a single-board computer.  I have no
particular goals in mind other than to try something "neat".  So, what
is likely to be the quickest, most foolproof way for me to get from
here to there?

I'm assuming I'll want an OS on the board for the runtime stuff.
Would one of the *BSDs or Linux be the way to go?  If so and given my
intentions, would there be a reason to choose one over the other?  My
contrary side wants to try a *BSD, but I have no experience in any of
them _or_ Linux.

And what about processor family?  I was thinking ARM or Coldfire or
PPC (something in the MPC5xx family maybe).  Again, would there be an
Ada- or OS-related reason to choose one over the others?

I did ask an abbreviated version of this question at the bottom of
another thread, but I'm hoping this thread will have more visibility.
So, is all of this do-able by a mere mortal?  Many thanks for any
advice!