The script flow.txt is the command sequence for synthesis, simulation,
P&R, DRC, LVS and GDS and CIF file creation.

The script syn_loop is the synthesis part which loops vasy, boom, boog
and loon to find the quickest netlist. The scripts vasy_loop etc do
each synthesis part separately. There are some timeouts to stop an
excessive run time which can be changed for a more exhaustive loop.

The loon loop alternates between the 0fF and 6fF wireload libraries
to find the netlist with the shortest critical path with the 6fF
wireload.

A script find_crit_path writes out the critical path for the 0fF and
6fF wireload libraries.

The placement from ocp is modified to insert a two track wide feedthru
cell at the left and right to ensure each cell row is properly
terminated with well and substrate tie downs. A script also merges
adjacent feedthru cells that are wider than 2 tracks.

Routing is done twice, once with metal-2 horizontally and once with
metal-2 vertically.

After routing the netlist, a script adds pieces of metal around the
vias to give a 2 lambda end overlap of metal. This can give DRC errors
to adjacent metal, so a loop runs DRC; adds layout blockages at the
DRC co-ordinates; and reruns the router with these blockages. The loop
continues until there are no more DRC errors.

This means that the layout can be DRC checked with vsc013.rds, which
checks for a 2 lambda via end overlap. The vsc013x.rds file which
checks for a 1 lambda via overlap has to be used on layout directly
written by NERO.

Critical path delay is 399 ps    (these numbers same as wsclib013)
Area is                552 um^2
Gate count              80
Occupancy               84%

The metal length numbers below are indicative only as segments are
not merged. The entire additional segment added around each via is
included, rather than the 1 lambda extra overlap. The number of vias
though is a true indication of the quality of the route.

                 wtclib013     wsclib013
               m2-ver m2-hor m2-ver m2-hor
length metal-1  2816   2770
       metal-2  4710   4266   4740   4426
       metal-3  3974   4614   4238   4624
numbers vias     126    136    136    136

The vertical metal-2 makes the best use of horizontal metal-1
routing in the vtclib013. For horizontal metal-2, metal-1 routing
between adjacent cells would be wrong-way.
One can see that the vertical metal-2 has the same number of vias as
horizontal metal-2 for the wsclib013.
For vertical metal-2, allowing horizontal metal-1 connections
reduces the number of vias from 136 to 126 or 7%.
