Getting Gates and Transistor count

[mickey4u]

I am new to Yosys and synthesis but what I want to achieve is to get the number of gates and transistors after the design unit has undergone synthesis. How do I achieve that?

[ZipCPU]

A couple of steps:

1. Read your files into yosys, using read -sv filename.sv. VHDL files may be read similarly when using the SymbioticEDA Suite.

2. Synthesize your design. For generic architectures, such as general ASIC gate counts, synth -top topmodulename is usually sufficient.

3. You'll then want to map to gates, using abc -g GATES. If you want some kind of special mapping, such as mapping to NAND and NOT gates plus FFs, then you can use abc -g CMOS2. See the help for abc within yosys for more information.

4. Finally, run the stat command to get the numbers of the various items used.

That should get you a number of gates. You'll need to do the gate to transistor mapping yourself.

Feel free to check out this article on ZipCPU.com for an example.

Dan

[mickey4u]

@ZipCPU Thanks. So Gates to transistor mapping is not supported. Any direction on how to achieve that.

[ZipCPU]

Depends ... how are the gates being implemented by your foundry? Seems like you'd kind of need to know that before you could go all the way to transistors.

[mickey4u]

@ZipCPU Okay. I will use the number of gates for now. What I want to achieve is, if I have multiple implementation of say an adder how do I select one the uses few number of gates or transistors.

[eddiehung]

Yosys maps to gates (via ABC) described in the Liberty format. The Liberty format has a attribute "area" which I think is used by ABC to make area-delay mapping decisions -- I presume this is the attribute used to capture transistor counts, so I suggest looking down that road?
You could look at the Yosys gate counts and multiply them by this area value, and/or you can get similar information from ABC, using ABC commands like print_stats...

[mickey4u]

@eddiehung Will do. Thanks

[cliffordwolf]

The Yosys stat command can also read a liberty file. If called with a liberty file it will output area numbers for the design.