Hi all I m attempting to run PEX on a 64bit width circuit us open-source-silicon.dev #xschem

Hi all, I'm attempting to run PEX on a 64bit width...

09/27/2023, 7:20 PM

Hi all, I'm attempting to run PEX on a 64bit width circuit using xschem (v3.1.0) + ngspice(v40+). The test bench is calling on a 37.6MB spice file generated by Magic(

ext2spice cthresh 0, extresist tolerance 10

). Loading the test bench is taking an excruciating long time, which it is still loading (start time: 02:57pm EST) the circuit. I have set within the

.spiceinit

file with

ngbehaviour=hsa

. Is there a way to speed up this process or a different way to go about this?

.spiceinit

Harald Pretl

09/27/2023, 7:24 PM

Why are you going with

cthresh 0

? I would think that something like

ext2spice cthresh 0.01

would be more than sufficient.

Harald Pretl

09/27/2023, 7:24 PM

Also, I do this

ext2spice rthresh 100

in my PEX script.

09/27/2023, 7:34 PM

Thank you for the advice! I was following a recipe posted on slack and do not have good insight to what values to use when doing PEX since I'm clueless. To my understanding

cthresh 0

within Magic equals to all possible parasitic capacitor, is that accurate? Is there a method to figure out what cthresh or rthresh values to use; if its trial and error, do you change the values based on circuit/simulation run time?

09/27/2023, 7:55 PM

This is the recipe I have used for PEX. Aside from

cthresh 0.01

and

extresist tolerance 10

, are there any settings that I should be looking out for?

Copy code

flatten cellname_flat
load cellname_flat
extract all
ext2sim labels on
ext2sim
extresist tolerance 10
extresist 
ext2spice lvs
ext2spice cthresh 0
ext2spice extresist on
ext2spice

09/27/2023, 8:18 PM

The PEX spice file size is 35.4MB, should I be worried or is there a target file size to aim for?

Harald Pretl

09/28/2023, 6:53 AM

There is no “proper” size for a PEX netlist. There is a “good enough” which you need to decide per application. See here a PEX script that we usually use, and it seems to work fine. https://github.com/iic-jku/osic-multitool/blob/main/iic-pex.sh

09/28/2023, 2:15 PM

Thank you for sharing the script. I will download and install the tools. Edit: Do I need to run

iic-osic-setup.sh

to be able to use

iic-pex.sh

properly?

Harald Pretl

09/28/2023, 5:21 PM

No, just run

iic-pex.sh

10/20/2023, 10:11 PM

Hi @Harald Pretl, I finally got around to properly use

iic-pex.sh

. I would like to ask whether I need to have the flat version of the cellname included or I can just use the hierarchal one? Plus, if full R-C mode produces a .spice file of 35MB, is this a point where I should give up on having the parasitic resistances included?

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