> After some more tests, I'm more confused than before.
> 
> Doing some thinking I suddenly vaguely remembered that the SA-110
> had a bug at some versions.
> 
> As mine is second hand, I had a look on it and seems to be a revision
> 'S'.
> 

Rev S is OK.  It's what I've got.  It's rev K that has the problems.

You should get the following message during boot with your chip.

cpu0 at mainbus0: SA-110 rev 3 DC enabled IC enabled WB enabled EABT

R.