Full-Custom FAQ

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I'm confused about the layers...

See the SCMOS Layer Guide for MOSIS processes.

See the FreePDK Contents for FreePDK layers.

My LVS doesn't match vdd! and/or gnd!

This has many possibilities. The most common are:

  1. You didn't make an inputOutput pin in the layout.
  2. vdd and vcc are not the same components. The "body" (well) of the transistors in our library (nmos/pmos) are assumed to automatically connect to gnd! and vdd!, respectively. If you use vcc instead of vdd, this will cause a floating net problem and LVS won't run. You can intentionally change this by using the nmos4/pmos4 devices that let you explicitly connect the body, but that should be unnecessary for this class.

Why does my extracted netlist seem disconnected?

Your designs WILL NOT PASS LVS if you use Create->Via. It will appear that the nets are disconnected if you try to highlight them in the extracted view. For example, your first level inverter output should connect to all the other FO4 poly gates. If you select the metal net in the extracted view and it does not highlight all the poly gates, you have this problem!

I get an error from DRC that an "edge is not on grid". Why?

I'm not sure how you made the shape, but shapes are required to be on a grid of 0.045. There is an option under the Options->Display Options to specify the x- and y-snap. Make sure this is set correctly, delete the offending shape, and redraw it.

When I run LVS, I'm getting the following error: Can't find/read file '.../LVS/si.out

This is the output of the LVS program. If it did not run, it didn't create this so when you try to view it by clicking the "Output" button, it will give this error. If this is the case, it should open another window. Click on the "Log" button... to see why the program didn't run.

The likely reasons are: 1) You didn't Check and Save your schematic 2) You modified your layout after running extraction.

My icfb crashed and I get a problem with a lock file now... what do I do?

Delete the obsolete lock files from a previous session. The lock file names are determined by adding ".cdslck" to the name of the file in the error message.

So for the file /home/aa/users/jdoe/CDS.log.1 the lock file is /home/aa/users/jdoe/CDS.log.1.cdslck

You can delete it with the UNIX command rm.

If there is an NFS lock file, you will need to kill the application and possibly log out and back in.

How do I draw a large numer of pins in layout? On a bus, for example.

There's a neat feature that is pretty to use called auto pin. When you Create->Pin.... input a bus name like A<0>. Check the box "Keep First Name". Do NOT select Auto Pin; leave it as Rectangle. Change the Y pitch to specify that they should be spaced out horizontally.

Select the layer you want to draw the pin on in the LSW. Draw a single rectangle that is the size you want all the pins to be. Place the label on the pin. After the click for the label, all the other pins will appear.

LVS fails to run with an error: "Cannot find switch master cell instance M0 in cellView (inv schematic) from viewlist 'lvs shematic gate_sch cmos_sch' in library '...'." Why?

You are not sourcing the class setup and missed this configuration variable:

export CDS_Netlisting_Mode=Analog

I want to use a behavioral Verilog model of part of my schematic. How do I do this?

All you have to do is create a functional view of the cell, by 'create cellview->functional' , or 'Design-> Create Cellview -> From cellview' in the schematic window, just like we create symbol. but now, we need to put a verilog model for the cell by editing the file that shows up in vi.

Then, when the netlister is run, it will show the views where it stopped. It will show, in icfb.log file, for example:

--------- --------- ----
trans_gate functional *Stopping View*
trans_gate_test schematic
---------- End Netlist Configuration Info ----------
*** Netlisting of cell - trans_gate_test, view - schematic successful.

And then simulation works OK. In this, each cell must be validated for correctness of its functional view. We can even put input-> output delays in the functional views.