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Answers to Top 10 Questions on Performing ECOs in EDI System

Comments(0)Filed under: ECO, LEC, synthesis, Encounter digital Implementation system, MMMC, tips and tricks, Cadence EDI System

Applying ECOs to a design can be complex, stressful and error prone so it's important to apply the right tools and flow to implement the changes successfully. EDI System provides multiple ECO flows to physically implement ECOs efficiently and accurately based on your design requirements. And adding a tool such as Encounter Conformal ECO Designer or the Encounter Timing System's MMMC Signoff ECO capability can lead to faster design closure with fewer iterations.

I field many customer questions related to implementing physical ECOs with EDI System. In this blog I provide answers to 10 of the most common questions. Do you have any tips to share on performing ECOs with EDI System? If so, please post it as a comment below.



1. What's the best place to find details on how to perform ECOs in EDI System?

The EDI System User Guide has a chapter dedicated to ECO Flows (Cadence Online Support access required). It describes several flows depending on whether it is a pre-mask or post-mask ECO, whether the changes are coming from a new Verilog netlist, DEF or ECO file, and whether gate array cells are being used or not. If you are new to ECO flows in EDI System then the ECO Flows chapter is the place to start!

It's worth mentioning here ECOs can be implemented using the super-command ecoDesign or by running each command individually (init_design, ecoDefin, ecoPlace, ...). Both methods are described in the User Guide.

2. What's the difference between a pre-mask and post-mask ECO flow?

A pre-mask ECO is when you are making changes to the design before any masks have been made. With a pre-mask ECO you are free to make changse to any layer thus providing you more freedom to implement the ECO.

A post-mask ECO is when you are making changes to a design after masks have been made. Therefore, you want to limit the changes to specific layers so you do not need to re-make all the masks. In a post-mask ECO flow you can utilize existing spare cells which where placed in the design to avoid changes to layers Metal1 and below. You can also instruct the router to which layers it can use to perform ECO routing and which must remain frozen.

3. How do I apply changes made in my RTL to the physical design through ECO?

Encounter Conformal ECO Designer is recommended for performing complex ECOs originating from RTL. It interfaces with RTL Compiler and EDI System to perform the logical and physical ECOs while leveraging Conformal's logical equivalency abilities to ensure the ECO was successful for both the front-end and back-end signoff.

4. How does EDI System identify spare cells in a post-mask ECO flow?

Spare cells should have a unique string in their instance name to identify them. Then the command specifySpareGate or ecoDesign -useSpareCells patternName is run to identify the spare instances. For example, if all spare cells have _spare_ in their name then they are identified using:

  specifySpareGate -inst *_spare_*


  ecoDesign -spareCells *_spare_* ...

Note if you are making manual ECO changes to a netlist and converting a spare cell to a logical instance, it's important to change the instance name. Otherwise, the instance may be identified as a spare cell if a future ECO is performed because it still has the spare cell instance name.

5. How does EDI System identify the changes in the design?

During the ecoDefin step the existing netlist (new netlist) is compared against the original placed and routed design. A summary of differences is output to the log file and a detailed report file is output to the local directory. You can review the report file to see a list of all the differences.

6. How do I use spare cells or gate array cells during placement?

Spare cells are identified using specifySpareGate. Then use the -useSpareCells true option when running ecoPlace to instruct it to swap the unplaced cells with spare cells of the same cell type:

  specifySpareGate -inst *_spare_*
  ecoPlace -useSpareCells true

Gate array style filler cells can be programmed with metal layers so the poly/diffusion and lower layers are not changed, and only the metal and via layer masks need to be modified. If you are using gate array spare cells the flow depends on the SITE type used by the gate array cells.

If your design has GA Cells which utilize a SITE type (i.e. GACORE) different from normal standard cells (i.e. CORE) then use:

  ecoPlace -useGACells GACORE

If your design has GA cells which utilize the same SITE type as standard cells:  ecoPlace -useGAFillerCells {List of GAFillerCells}

Reference the User Guide for the complete flow.

7. Is ecoPlace -useSpareCells true timing driven?

ecoPlace will choose the spare cells to minimize wire length but is not timing driven. After ecoPlace you can run ecoSwapSpareCell to relocate an instance to the location of another spare cell of the same type. Alternatively, you can run ecoRemap in place of ecoPlace. ecoRemap is timing driven and automatically analyzes the functionality of the newly added cells and remaps them to available spare cells. The software analyzes the logic and performs changes to improve timing and minimize DRVs.

8. How do I freeze certain metal layers during routing?

In a post-mask ECO Flow run ecoRoute with the -modifyOnlyLayers option to specify which layers it is allowed to modify. For example, to route using only Metal1 through Metal3:

  ecoRoute -modifyOnlyLayers 1:3

9. How does ECO routing deal with metal fill?

When performing a post-mask ECO flow, ecoRoute will ignore the metal fill while routing. This will likely cause DRC violations between the ECO routes and metal fill. To fix these violations, run verifyGeometry followed by the the trimMetalFill command. This will cut back the metal fill from the ECO routing to fix the violations.

10. Does EDI System support interactive (maual) ECOs?

Yes, EDI System provides a number of interactive commands to both evaluate and commit ECO changes. See the Interactive ECO chapter of the EDI System User Guide for details.

When performing interactive ECOs make sure setEcoMode is set as desired. Here are some specific options to pay attention to and tips to speed up run time when implementing a series of ECOs:

  setEcoMode -updateTiming - Default is false allowing you to wait until all ECOs are performed to run timing analysis. If set to true, timing analysis is run after each ECO command.
  setEcoMode -honorDontTouch, -honorDontUse, -honorFixedStatus - The default for all of these is true. So if you find you cannot make a change, check if any of these apply.
  setEcoMode -batchMode - Sets this to true to improve runtime if you are performing many ECOs.



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