A simple router that takes advantage of the fact that in each cell with
DFFs their CLK inputs can directly connect to the global clock network.
Networks with a large number of such sinks are sought and then each
network is assigned to the available independent global clock networks.
There are limited possibilities for routing mixed networks, that is,
when the sinks are not only CLKs: in this case an attempt is made to use
wires such as SN10/20 and EW10/20, that is, one short transition can be
added between the global clock network and the sink.
* At this time, networks with a source other than the I/O pin are not
supported. This is typical for Tangnano4k and runber boards.
* Router is disabled by default, you need to specify option
--enable-globals to activate
* No new chip bases are required. This may change in the distant future.
Signed-off-by: YRabbit <rabbit@yrabbit.cyou>
