Multi-part path makes cadence hang?

We have seen problems with Multi-part paths (MPPs) with lots of contacts. The larger we make this path, the more contacts the MPP has to maintain, the slower things ran in our session. We finally ended up writing some wrapper code for flattening MPPs. We determined that ultimately we wanted our symbolic contacts placed instead of the sub-rectangles of an MPP, so when we flatten the MPP, we replace the rectangles with symbolic instances. We then decided that since our flatten code does this automatically, we modified our large MPPs to no longer have sub-rectangles in them. We use a temp layer and draw it as a sub path in the MPP. We can still stretch and chop the MPP as usual. When we flatten the MPP later on, we convert the temp layer to contact instances. Stretching and reshaping an MPP with 8 to 10 sub-paths is much more efficient than dealing with thousands of sub-rectangles. In general, we found that all of Cadences ROD objects add a performance hit (we used to use a lot of these in our pcells). The ROD objects are useful, but sometimes you have to use them sparingly so you can take advantage of the features only when it is needed.

 -Derek

Hi Derek, thanks for the indepth reply. I'm finding that my narrower mpp's, say with ONE row of contacts/vias, are ok. The wider ones won't get used as often, so we might be able to live with it. I'll see how much the other engineers complain when they use them. i just did a quick estimate and some of these guard rings have around 15,000 contacts, perhaps this is too excessive for cadence to handle, who knows. 

 Hi Stu,

You could consider re-implementing the MPP as a PCell; use the enterPath function to gather the points and provide a "rubber-band" outline of the guardring/path, you will not see the details this way, only the outline. Inside the PCell you could use rodFillBBoxWithRects() to create the contact shapes as regular dbObjects without the ROD overhead.  I wrote a MultiPartPath example that uses enterPath to gather the points and then pass on to a creation function (in that case it was not a PCell, but a wrapper to the rodCreatePath() function).  In fact what I am suggesting would not have to be a PCell, you just have a drawing routine that perhaps uses an MPP for the path parts and rodFillBBoxWithRects() for the contact parts.

Look in SourceLink for CCSslotMetal() for the example I mention above. How can I create slotted metal paths?

Hope this helps!

Regards,

Lawrence.

Hi Lawrence, thanks for the info. I've not had try at this yet but i will get round to it.

Thanks

Stu