[Libre-soc-bugs] [Bug 413] DIV "trial" blocks are too large

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Thu Jul 2 20:11:56 BST 2020


Jacob Lifshay <programmerjake at gmail.com> changed:

           What    |Removed                     |Added
                 CC|                            |programmerjake at gmail.com

--- Comment #1 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #0)
> the "trial" blocks used in the div pipelines create 2.1 megabyte VHDL
> files each, during layout, and there are 270 of them.  this results
> in a jump in the size of the BLIF file from 10 megabytes to 100 megabytes,
> and a jump from 85,000 blocks (which coriolis2 can cope with)
> to 500,000 (which it cannot).

yeah, I'm aware the div pipeline is currently too big. I'm planning on
rewriting it to shrink it by a large factor. For now, we can change the number
of bits calculated per pipeline stage to 1, which should reduce it to 3/8 the
current size. The downside is that takes 64 compute stages (32 pipeline
stages), so, for now we'll just have to live with not being able to keep the
div pipeline full due to limited fu count.

To do that, set log2_radix=1 here:

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