DRC errors in detailed routing - "Metal spacing violation"

[oharboe]

I think this is happening because two macros that need straight vertical wires between them don't have IO pins lined up and then the wires between the macros are criss-crossing.

What is the difference and purpose of MACRO_PLACE_HALO vs MACRO_PLACE_CHANNEL and where do I use them, in the macro or where I'm using the macro from?

Some thoughts on what I might do:

• I could modify the halo macro to have a big enough "halo" (black area) where the wires can move horizontally to line up better with their destination pin in the other macro.
• I could fix the io pin locations and floorplan so the router is able to use straight vertical wires instead of crisscrossing between two macros. This would reduce the need for a big halo.

[vijayank88]

@oharboe
Variable description found here: https://openroad-flow-scripts.readthedocs.io/en/latest/user/FlowVariables.html#floorplan

[oharboe]

Yes... but I'm wondering what it means?

I can increase the "halo", but what is a halo and what effect does it have? Do I specify this on the macro in the config.mk where I instantiate the macro.

Same for MACRO_PLACE_CHANNEL.

MACRO_PLACE_HALO	horizontal/vertical halo around macros (microns).
MACRO_PLACE_CHANNEL	horizontal/vertical channel width between macros (microns).

[vijayank88]

It is useful where automatic macro placement technique used.
If you're using manual macro placement above variable not in effective.
HALO/CHANNEL provide enough space for routing and where std cells not placed.

[oharboe]

I see. I am still not clear on the distinction between channel and halo though.

[maliberty]

Note that mpl distinguished halo vs channel but mpl2 just uses halo. The distinction is that a channel is the space between two macros but the halo applies on all sides of the macro.

I can't tell much from the picture.

[oharboe]

From your explanation, I would have thought that you specify either HALO or CHANNEL and that HALO took just one integer?

export MACRO_PLACE_HALO = 10 10
export MACRO_PLACE_CHANNEL = 20 20

[maliberty]

The setting are for x & y separately. Usually they are the same

[oharboe]

Then I'm still confused about the difference between MACRO_PLACE_CHANNEL and MACRO_PLACE_HALO.

[maliberty]

Imagine channel=10 and halo=5. Then macros must be 10 apart but standard cells must be 5 away from a macro. It is moot with mpl2.

[oharboe]

Updated docs in pull request based on the above: The-OpenROAD-Project/OpenROAD-flow-scripts#1007