IO Position Control

[heaton56]

How are the IO positions controlled?

I was testing progressively increasing the density of the gcd example design until it broke.
When I reduced the CORE_AREA = 10.07 11.2 52.25 39.2, I noticed it no longer routed IO at the top.

Hence the question: how to control the IO positions?

[maliberty]

You can read about set_io_pin_constraint in https://github.com/The-OpenROAD-Project/OpenROAD/tree/master/src/ppl

[rovinski]

To expand, you can use put PPL commands into a script, then use that script in the flow by setting in your design config:

IO_CONSTRAINTS = path/to/your/script.tcl

You can also provide additional arguments to the pin placer with:

PLACE_PINS_ARGS = argument1 argument2 ...

There is also an option to use a pre-floorplanned DEF file by setting:

FLOORPLAN_DEF = /path/to/your/floorplan.def

[maliberty]

It places the IO to minimize wire length. Since you have no instances near the top you it is unsurprising that you have no IOs there.