How to P&R a design using custom cells in Cadence Encout

rtl compiler set_dont_use avoid

Hi folks,
Instead of using standard cells, i want some custom cells to be used in placement and routing of a design. Is there any tutorial or way to do that.

Also if i want certain specific standard cells to be used, how can i do that in Cadence Encounter.

Any pointers, tutorials, links shall be really appreciated.


Thanks

Kind Regards,

set_dont_use cadence

Instead of using standard cells, i want some custom cells to be used in placement and routing of a design.

Click to expand...

Hi,

Let's start with a design which is currently in the RTL stage and needs to be P&R'ed. The steps to use custom cells in your design would likely be:

1. Create a library containing your custom cells. Remember you need to create two types of libraries- a logical library, called .lib which contains data like timing, power consumption etc. of the custom cells and a physical library, which contains the physical data like size, shape etc. of your custom cells. This means you should have characterized your custom cells prior to creating the libraries.

2. Next perform synthesis on your RTL code. While doing this, map your design to the logical library which you have created from your custom cells. The output of synthesis is a gate-level netlist.

3. Then perform P&R on the gatelevel netlist. For this you need to append the physical library to your design, i.e. provide the P&R tool with the physical library to perform P&R of your gate-level netlist.

All through I have assumed you are adopting the top-down approach; the fact that you are using a P&R tool suggests that. As I see it, in the bottom approach, you would place and route your standard cells manually and possibly without creating a library containing them.

Hope I have answered your query, i.e. if this was what you wanted to know.
Also do correct me if there is some anomaly.

Is there a way or tool to characterize custom cells. I mean tools that can generate .lib and physical library.

Is there a tutorial or project or paper that describes the whole flow? The fact that you know about it tells me that there is material out there. Could you help in sharing the material which could be a tutorial or a project or a paper.

Also i had asked in the second part of my problem on how to restrict cells in P&R. That means to P&R a design with certain specific standard cells are used only.
For example if the design is of a full adder, i just want 2 input AND and OR Standard cells to be used and not XOR Standard cell.

Thanks a lot.

To your second question about how to restrict the cells in p&R :

you can use command similar to set_dont_use command in synopsys-DC which will tell which kind of cells u dont want to use for your design

u might have different drive strengths for AND gate itself, u can specify the particular drive strengths which you dont want to use for place and route

dcreddy1980!
can you elaborate on how to write such commands for Cadence Encounter? Any pointers, links ??

Thanks

Re: How to P&R a design using custom cells in Cadence En

Is there a way or tool to characterize custom cells. I mean tools that can generate .lib and physical library.

Click to expand...

I am not sure if tools that characterize custom cells exist, but I guess its a very hectic process when done manually. You need to change a lot of parameters (PVTs) and see how the cell reacts to them etc. Will let you know if I get any more info on the same.

Is there a tutorial or project or paper that describes the whole flow?

Click to expand...

The complete flow would be a very elaborate one with a lot of details coming in. I haven't come across a very detailed one, but we guys did make one during my certification program. Gimme a few days, I'll dig it out for you.

how to restrict cells in P&R. That means to P&R a design with certain specific standard cells are used only.
For example if the design is of a full adder, i just want 2 input AND and OR Standard cells to be used and not XOR Standard cell.

Click to expand...

Well for this you'll have to restrict cells to be used in your design while performing synthesis, because when you P&R your design, the tool identifies the cells present in your gate-level netlist, goes to the physical library, picks the physical data of those cells (like shape and size) and places the cell.
So, if you want to use only AND and OR cells in your full adder and not XOR cells, you should place a restriction on cells to be used while performing synthesis on your RTL netlist of your full adder. The cells to be used in your design are finalized at the synthesis stage; after that you don't have control on the type of cells in your design.

The experienced fraternity, do give your views on this. Hope what I've said is correct.

waiting to see what you did. Please do dig out.

Re: How to P&R a design using custom cells in Cadence En

tariq786 said:

Is there a way or tool to characterize custom cells. I mean tools that can generate .lib and physical library.

Click to expand...

You can use signalstorm Library characterizer (slc) for creating .lib files and abstract generator for .lef files.

tariq786 said:

how to restrict cells in P&R. That means to P&R a design with certain specific standard cells are used only.
For example if the design is of a full adder, i just want 2 input AND and OR Standard cells to be used and not XOR Standard cell.

Click to expand...

You can use set_dont_use command in your sdc file or "avoid" command in RTL Compiler at synthesis to avoid the cells during mapping.

Re: How to P&R a design using custom cells in Cadence En

varunvats69 said:

Is there a way or tool to characterize custom cells. I mean tools that can generate .lib and physical library.

Click to expand...

I am not sure if tools that characterize custom cells exist, but I guess its a very hectic process when done manually. You need to change a lot of parameters (PVTs) and see how the cell reacts to them etc. Will let you know if I get any more info on the same.

Is there a tutorial or project or paper that describes the whole flow?

Click to expand...

The complete flow would be a very elaborate one with a lot of details coming in. I haven't come across a very detailed one, but we guys did make one during my certification program. Gimme a few days, I'll dig it out for you.

how to restrict cells in P&R. That means to P&R a design with certain specific standard cells are used only.
For example if the design is of a full adder, i just want 2 input AND and OR Standard cells to be used and not XOR Standard cell.

Click to expand...

Well for this you'll have to restrict cells to be used in your design while performing synthesis, because when you P&R your design, the tool identifies the cells present in your gate-level netlist, goes to the physical library, picks the physical data of those cells (like shape and size) and places the cell.
So, if you want to use only AND and OR cells in your full adder and not XOR cells, you should place a restriction on cells to be used while performing synthesis on your RTL netlist of your full adder. The cells to be used in your design are finalized at the synthesis stage; after that you don't have control on the type of cells in your design.

The experienced fraternity, do give your views on this. Hope what I've said is correct.

Click to expand...