Committed vias were checked for hole spacing, but a route's own vias are
not committed until it is done, so a route hopping layers (more of them
on 6 layers) could put two of its vias 0.41 mm apart, as th-eda's
6-layer flight controller showed. A via is now also checked against
layer changes earlier on its own route.
A fixed via sits anywhere, not on a cell centre, and may have a bigger
drill than the router's via; checking hole spacing between cell centres
with one drill let the flight controller's routed 0.2 mm via come 0.19
mm from a hand-placed 0.25 mm one. The board now carries each fixed
via's drill (from KiCad's padstack name), and cells are checked against
fixed vias exactly.
A route could drop a via next to (or onto) a through-hole pad of its own
net, where it changes layer for free, and a via reusing a fixed via's
cell came out a little off the fixed via's centre, beside it. No via now
goes within hole spacing of a through-hole pad of any net; a via in a pad
is checked exactly against every via and hole; and a routed via on a
fixed via of its net is not written. charge-sense: 4 hole_to_hole to 0;
flight controller: 2 to 0, unconnected unchanged.
The exact engine rebuilds its output from each connection's own vias,
so connections sharing a plane via each wrote a copy: th-eda's flight
controller had 71 spots carrying 2 to 4 vias of one net. Vias are now
written once per net and spot, and never on a via already on the board.
Every pin of a supply drops its own via to the plane, and nothing kept
two of them apart: the flight controller came back with 199 co-located
holes and 109 hole-to-hole errors, nearly all VDD_3V3 and GND. A via now
keeps its drill plus --hole-to-hole (default 0.25 mm, KiCad's) from
every via centre, fixed ones included, except an own-net via at the same
cell, which it reuses; such a via is written once, and none is written
on top of a via already on the board.
rsp2k