# DRC errors in detailed routing - "Metal spacing violation"

Tool: Detailed Routing

Subcategory: DRC violation

## Conversation

### 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.

![image](https://user-images.githubusercontent.com/2798822/233312554-d99551bf-439f-47f9-85da-21b601517284.png)



### vijayank88
@oharboe 
Variable description found here: https://openroad-flow-scripts.readthedocs.io/en/latest/user/FlowVariables.html#floorplan

### 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.

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

### 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: https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts/pull/1007