Magic - Design Rule Checking using Cadence Assura (via Cadence Virtuoso)

Convert Magic designs to Cadence database format

Cadence and Magic use different file formats for the storage of design data.
Interchange is possible via a common GDS2 stream format.

Procedure

go to magic directory e.g.

  hind2<~>$ cd ~/design/magic/c35b4/cell_lib

translate magic file to cadence format
```
  hind2<~/design/magic/c35b4/cell_lib>$ do_c35b4_cellin <cellname>
```
cell cellname (in file cellname.mag) and all sub-cells will be translated.

Design Rule Checking using Cadence

The Magic layout editor supports simple on-line DRC.
The Cadence layout editor supports a DRC post-processor.

Magic designs must pass the more stringent Cadence DRC before they will be accepted for fabrication.

Procedure

Change to directory containing cadence files

  hind2<~/design/magic/c35b4/cell_lib>$ cd ~/design/cadence/c35b4/cell_lib

Start cadence virtuoso via the ams_cds script
```
  hind2<~/design/cadence/c35b4/cell_lib>$ ams_cds -tech c35b4
```
ams_cds is a wrapper script supplied by Austria Micro Systems (AMS) which sets up the design environment and then calls the cadence virtuoso tool. It is part of the AMS 'HIT-Kit' design kit.
Use the library manager for library, cell and cellview manipulation
```
  Tools -> Library Manager...
```
Within the library browser the left hand mouse button is used for navigating around the library structure while the right hand mouse button provides access to the commands used to manipulate the libraries, cells and cellviews.
- Open the imported design for edit
  
  Use the mouse to select Library: cell_lib, Cell: <cellname> and View: layout then invoke the open command -
```
  File -> Open...
```

Perform DRC with default options for technology c35b4c3

  Assura -> Run DRC...

    Run Assura DRC
      Technology        [ c35b4c3                  -]
    OK

Once the DRC run is complete you should accept the offer to view the results.
Within the error layer window you can select different error types on the left, different cells on the left and zoom to individual errors using the left and right arrows.
If the only error type that is listed is an "INFO" message ("INFO: C35B4/C35B3 ASSURA DRC DECK ...") then the system has detected no errors.
If you find errors you will probably have to modify your original magic design

Note that when you are learning how to use the Cadence DRC facility, it is best to check a magic design created with known errors. You can then track down the same errors using Cadence DRC.

Additional Documentation

All Cadence documentation is available on-line via 'cdnshelp'. Unfortunately each Cadence install has a separate 'cdnshelp' installation. To get around this problem you can use the following command to invoke the appropriate 'cdnshelp' command for a particular cadence executable:

cdnshelp_for <cadence_executable>

For this tutorial, the most appropriate commands are:

cdnshelp_for assura

which enables you to get help on all Cadence ASSURA tools and:

cdnshelp_for virtuoso

which enables you to get help on all Cadence IC6 tools.

(note that 'cdnshelp_for ams_cds' won't work since 'ams_cds' is an AMS design kit command rather than a raw Cadence command)

On-line manuals of particular interest to this tutorial are:

Assura Physical Verification User Guide

Virtuoso Layout Suite XL User Guide

Full Design Rules for the AMS c35b4 process are also available via the Design Rule Documents web page.

Iain McNally

27-11-2017