A route may not leave a cell inside a wire keepout as a wire, nor reach
a pin there by one: it changes layer instead, and the via goes in the
pad. A pin whose every stub enters a keepout is reached by a via only.
A structure keepout named rule_area... (mckicad names KiCad rule areas
so) is checked for overlap only, as KiCad's DRC does, with the free ends
of each wire tested for their round caps.
--access-cost C makes a route pay C to pass where it would close another
pin's way out (its end cells, the via it may need there, and the
clearance around both) while that pin still has connections to route.
A pin inside a wire keepout can only leave by a via; its stub to the
cell centre was track inside the keepout, which the exact check refused.
The via now goes on the pin itself. Pin stubs are also checked exactly
against wire keepouts, as the exact engine will check them.
bench/diagnose.py reports what each refused connection collided with.
rejected by the exact check, unroutable even alone, walled in (a pin's
free region is closed off by other copper, with the nets that close it),
or congestion. The board state is the best pass's, rebuilt by replaying
its paths.
Runs every board with every variant under the same seeds and compares
them seed by seed, so a change is judged against the routing-order
noise rather than one lucky or unlucky run.
rsp2k