> The garbage is probably because the oscillator frequency is wrong.
> The driver tries to use 25Mhz, but I bet the prom 'clock' property
> is set to a non 25 value

For a moment I thought this was a discussion about sBus expansion
kits (card, cable and chassis with another half dozen sBus slots).
If you find one of those apply a large hammer to it before anyone
tries to use it.
They don't (can't) work reliably.  Something to do with the sBus
not allowing wait states in the address phase of the cycle.  In
order to squeeze enough time for the extra logic delays they have
to generate a clock that preceeds the main sBus clock by a few ns!
This requires a CBU (Crystal Ball Unit)...

    David