[Eda-dev] Silly question about units: gates vs. cells

Tim Edwards tim at efabless.com
Mon Jul 8 08:26:04 EDT 2019

Hello Øyvind,

 > "number of cells" - how does that translate to "gates".
 > The design limit size for qflow is currently on ~30000 gates, right?
 > I'm running my biggest test yet w/qflow:
 > [deleted]
 > Fixed density planning, density = 0.1
 > Number of cells = 51825, total width = 25901560
 > Width of fill = 233114040
 > [still running, I plan to give up if it doesn't finish overnight]

Not a silly question at all, because the answer depends on context.
I should qualify that the approximately 30k gate limit on qflow before
tools like graywolf and qrouter get bogged down is a number that
excludes any fill;  for graywolf, fill cells are glommed together with
the "active" cells, so the total number does not include the fill cells.
Qrouter sees all the cells, but the qrouter limit is defined more by
the total number of routes than the total number of cells (although
added fill cells make the design larger, which has some impact on the
runtime of the router, but the largest impact is due to wire congestion).

In the output of the "decongest" script above, you have a base number of
cells (not counting fill) of 51825.  So yes, you are pushing the limits
of the tool.

But note that when I say "limit", there are no hard limits to the tools.
There are just certain routines that have exponentially rising runtimes
that tend to kick in somewhere around the ~30k gate count.  For both
graywolf and qrouter (the two "long poles in the tent"), you should be
able to get a general idea of how fast each is progressing, and whether
the runtime is going to be hours, days, or weeks.

I hope that by the end of summer I should have enough bits of the
Open Road tools integrated into qflow that such problems will no longer
be a concern.  This is a very high priority for me.


| R. Timothy Edwards (Tim)       | email: tim at efabless.com             |
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