[755-1] Accusim simulation speedups

[Konstantinos Dovrolis <dovrolis@cs.wisc.edu>]

Folks

If the post-layout full-system simulations take too long,
you can make them faster, reducing their accuracy. I will
mention a couple of ways to do so, although there are many
more. Use these features carefully, though. Faster simulations
are more "digital" simulations, which means that certain
things that may go wrong (say due to charge sharing) may not
be visible after a certain point.

The general Accusim menu that controls this stuff is in: Setup->
Simulator Options. Especially, the MOS SWITCH template allows
you to specify different simulation models for the MOS devices.
Most of these models can lead to faster simulations, as long
as the ciruits are purely digital. I suggest the Switch,
or Analytic, or AutoSwitch models. 

Another approach to speed up the simulations is to 
reduce the number of "keeps". Accusim by default stores
internally the voltage waveform for each node in the system,
which may cause huge memory requirements. You can select the
nodes that have to be monitored, using the menu: Setup->Keeps.

There are other ways as well, but I suggest that we use them
only if needed. So if the simulations are slow even when you do the above, 
please see  or email me.

Also, please note any such speedups that you used in your report.

C.