Special Router to connect std cells to power rings

[Wen-Tian-Pineapple]

Description

As described in #2209 and #2349, in the design that involves multiple voltage domains, there is no routes from standard cell to another voltage domain that is generated by pdngen. We address this issue and created an issue in OpenROAD #3050

Suggested Solution

Qianxu and I from the openfasoc team created a PR #3043 to address this issue. Currently, it is able to connect the standard cells to power rings. See details in OpenROAD #3050

Proposed Command:
All of these commands should be called before global route.
dbGPpins : create [dbBlock] [dbTech] [source net name] [number of connection points] [position]

odb::createConnection [ord::get_db_block] [new net name] [instance name] [iterm on power ring to check the connections]
Currently this command creates custom connections from a specific cell to the power ring before global route.

temp sense generator exmaple with 1 PGpin on power ring VIN (More example in #3050
odb::createPGpins [ord::get_db_block] [ord::get_db_tech] "VIN" 1 "default"
odb::p2proute [ord::get_db_block] "pg_VIN" "temp_analog_1.a_header_0" "VIN"
odb::p2proute [ord::get_db_block] "pg_VIN" "temp_analog_1.a_header_1" "VIN"
odb::p2proute [ord::get_db_block] "pg_VIN" "temp_analog_1.a_header_2" "VIN"

Future Work:

1. set_routing_layers [-power minLayerName maxLayerName] for power connection.
2. Additional ndr rules [-multicut via]. May need further modification in detail router.