Re: Why do you need to route clock seperately
I suspect two things.
One, that the folks in the ASIC (digital) sections would
be of more use to you.
Two, that maybe it has to do with the clock being a
(or the most) critical timing resource, its chip-wide
consistency is important enough to give its routing
and loading priority over data and control signals.
If the P&R tool can't handle it (and making it try,
while doing all the "other 99%", would be asking a
lot and leaving a lot to chance or the competence
of the tool and its operator) then maybe the P&R
can at least be taught to respect a specially built
clock network's cells and routes, leave it alone and
give it some space.
Clock uncertainty has to be accommodated in the
timing analysis / closure. Squeezing it out leaves
more slack for the rest of the mess.