Standard Parasitic Exchange Format (SPEF) Format – Part 1


So, this has been due for long time. May be because of tight tape out deadlines, this very important piece of Physical Design flow just got missed.

And I am sure, like me, many might be curious to know what is the IEEE SPEF format, what does various attributes of SPEF file represent,how to generate spef file, etc… So, here you go.

Finally got time to make video on IEEE SPEF format. Let’s nail this down, with below example design, which I have been using on Udemy

We will take a piece of the circuit and write the SPEF file for a piece of input port and net

Let’s write down the path components of Input port Din2 in SPEF format, which will also be a part of large SPEF file

In the above SPEF equivalent “I” represents input port

We can also map the Din2 port with a number, (say *1, as in below example), and use*1 as reference for Input Port Din2. So, wherever, we have *1 in SPEF file, it is nothing but Din2 port. This technique greatly reduces SPEF file size

This becomes one part of the SPEF file

In the next post,we will extract the net connected to Din2 (shown below) and write a SPEF format of the same

We are not done yet. We need to define header for this file, we need to define units for slew, load, resistance, time., and lot more

Ever heard the saying “An ounce of patience is worth a pound of brains”, we will follow the same 🙂

Let’s go slowly and continue from this point on-wards. Till then, may be “revise and relearn”

Happy Learning!


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