Chapter 9: Tools
||9-7: Network Consistency Checking (NCC)
To run NCC, use these commands (in menu Tools / NCC):
- Schematic and Layout Views of Cell in Current Window
Use a heuristic to figure out what to compare against the cell in the current window.
If the current cell is a schematic then compare it against some layout cell in the same cell group.
If the current cell is a layout then compare it against some schematic cell in the same cell group.
Since most cell groups have one layout cell and one schematic cell,
this form of the NCC command is usually the most convenient.
NCC expects that all layout cells in given group match the corresponding schematic cells found in the that group regardless
of the dependencies between them.
- Cells from Two Windows
Compare the two cells that are displayed in the two opened windows
(there must be exactly two windows).
This is useful when the schematic and layout are not in the same cell group.
The command can also be used to compare schematics with schematics or layout with layout.
However, the command will not compare icon cells since they don't have connectivity.
- Run NCC for Schematic Cross-Probing
This command runs NCC and saves the net associations between schematic and layout.
The user can generate a Spice netlist (for example) from an Electric layout cell.
Simulating this netlist will result in a waveform file that uses layout hierarchy and net names.
If this waveform file is loaded into Electric, it cannot be cross-probed from the schematic.
It can be cross-probed from the layout, but that is often difficult to do.
In this case, the user can run this NCC command,
which will save net associations between schematic and layout.
Then, the user can cross-probe from the schematic,
and Electric will automatically translate the schematic net
to the appropriate layout net contained in the waveform file.
These commands control NCC and analyze its results:
- Copy Schematic User Names to Layout and Copy All Schematic Names to Layout
For each pair of matching schematic and layout cells,
rename networks and nodes in the layout cell to have the same name
as the equivalent networks in the schematic cell.
The first command copies only user-assigned names from the schematic to the layout;
the second command copies all names.
Furthermore, it only changes the names of layout networks and nodes that have no user-assigned names.
If a layout network or node has a user-assigned name that does not match the schematic
then this command prints a warning.
This command also warns when non-equivalent networks or nodes have the same user-assigned name.
- These commands use the result generated by the most recent run of NCC.
That NCC run should be hierarchical without size checking.
- These commands clear the saved result from the last run of NCC.
If you need to run a command that needs the last result, for example "Highlight Equivalent",
then you must rerun NCC.
- Highlight Equivalent
Highlight the network or node that is equivalent to the currently selected network or node,
using the result of the most recent NCC run.
The user should be aware of a number of limitations:
- This command works best for networks in the top level cells compared by the most recent NCC run.
- This command also works for nodes in the top level cells
compared by the most recent NCC run as long as those nodes are primitive transistors
or were treated as primitives because NCC compared them hierarchically.
- Because NCC combines MOS transistors that are in series into a single NMOS_*STACK,
NCC can't find equivalents for certain networks and nodes.
For example, when NCC merges two series MOS transistors into a single NMOS_2STACK
it removes the network between them from NCC's database.
Therefore if you click on that network and ask to highlight the equivalent,
NCC won't be able to find an equivalent.
- Because NCC combines MOS transistors that are in parallel,
it can't find equivalents for certain networks and nodes.
For example when NCC detects two parallel MOS transistors,
it removes one from NCC's database but adds it's width to the other.
Therefore if you click on the transistor that was discarded and ask to highlight the equivalent,
NCC won't be able to find an equivalent.
- Add NCC Annotation to Cell
This is a submenu that allows user to select which NCC annotation to add to a cell.
Note that the designer should replace text surrounded by angle brackets: "< >".
See Section 9-7-4
on "NCC Annotations" for a description of each NCC annotation.