SPECTRE-18023: Parasitics RC reduction disabled (fast APS)

Hi All,

I generally need to use fast APS (++aps) and parasitic reduction (++parasitics) options when running postlayout simulations with Spectre, in order to cut simulation times to manageable levels.

Now, I am suddenly getting the following warning in some cases:

WARNING (SPECTRE-18023): Parasitics RC reduction is disabled. Possible reason could be 'preserve_inst=all' is defined in the option statement

I also see that the simulation times are massively longer as a result. 

1) I am not specifying the option preserve_inst at al. Here's an extract out of my netlist:

simulatorOptions options reltol=1e-5 vabstol=1e-6 iabstol=100e-12 \
    temp=125.0 tnom=25 scalem=1.0 scale=1.0 macromodels=yes gmin=1e-12 \
    rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e-3 \
    sensfile="../psf/sens.output" checklimitdest=psf ignorezerovar=yes \
    colonasdelimiter=none

2) The situation doesn't seem to change even if I explicitly force preserve_int=none.
The above warning does not always seem to appear, but I don't know the exact cause/effect mechanism.

3) I am using MMSIM 15.10.284. Here's an excerpt from my spectre.out log showing the run options used

/cadence/mmsim/15.10.284/tools/bin/spectre  \
        -64 =log spectre.out ++aps ++parasitics=conservative +mt=8 =mdl  \
        mcarlo.mdl input.scs -raw psf -measure measure

4) I am running TRAN analysis with errpreset=conservative

5) The errpreset options, the standard simulator options are something I use as a default for everything that I run, and it seems as if parasitic reduction works for some cases and not for others, i.e. different netlists, different simulation setups.

Has anyone faced a similar issue? Any workarounds would be most welcome.

Thanks,

Vivek