( ESNUG 266 Item 3 ) -------------------------------------------- [9/18/97]
Subject: (ESNUG 264 #7 265 #4) Efficient/Cheaper Use of Synopsys licenses
> I now know further that the HDL Compiler is sometimes invoked during Hi
> Level Optimization (HLO). Since HLO is invoked in the beginning of
> compilation, the HDL Compiler license will be checked out all along the
> compilation which means you have to have 1 HDL Compiler per 1 Design
> Compiler license. The question now is - how often HDL Compiler is used
> during HLO?
From: Vickie Moore <moore@minim.sps.mot.com>
John,
This may be helpful:
hdl_keep_licenses = "false"
When this variable is false, hdl licenses are released during execution of
compile, after compile has completed the subtasks that require the license.
- Vickie M. Moore
Motorola
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From: [ Someone Inside Bill & Dave's Old Company ]
John,
Before you spend too much money on HDL licenses look at the man page for
'hdl_keep_licenses' (defaults to true). We have been using about a 2:1
ratio of Design-Compiler to HDL licenses without any issues. Our scripts
do the following:
Wait for an HDL license.
Read in HDL
Give up HDL license
Compile
If the compile grabs another license the 'hdl_keep_licenses = false'
will ensure that it is released as soon as possible.
Please keep me anon.
- [ Someone Inside Bill & Dave's Old Company ]
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From: Victor_Duvanenko@truevision.com (Victor Duvanenko)
John,
This is in reply to using fewer (V)HDL readers than Synthesis licenses.
I've been runing in this mode for the last 5 years (since Synopsys 1.5)
and have complained about Synopsys not being frugal with licenses, which is
the mode that they test under, but is not the usage mode of the (smaller)
customers. Before DesignWare, writing scripts to wait for (V)HDL reader
and then reading in your source code, and then removing (V)HDL reader
license used to work perfectly fine. Then when DesignWare came out,
Synopsys needs to check out the (V)HDL reader to synthesize some of the
parts (which are written in a technology independent way - i.e. some using
(V)HDL source). At that point (which is after the "compile" command), the
(V)HDL reader is grabbed and then is never released. The "compile" command
gets done with DesignWare and then goes on to the optimization stage, but
does not release the (V)HDL reader. Thus, removing license after you read
in your (V)HDL source may not be enough, since the first time that Synopsys
needs to make you a 28-bit incrementer it may need a (V)HDL reader, but in
the subsequent runs it may not. This introduced enough uncertainty into
the license scheme to cause some customers to complain a lot (those with
little $$'s) and some to buy more (V)HDL readers (those with more $$'s).
With all this "history" summarized, is there anything an engineer can do?
Yes, in the 1997.08 release there is a new variable "hdl_keep_licenses"
that you can add to your .synopsys_dc.setup. By default, for backward
compatibility reasons, it is set to true. So, you should set it to
"hdl_keep_licenses=false", and magically the (V)HDL reader will be given up
after DesignWare is done. Synopsys documentation has a mistake in it, they
refer to "hdl_keep_license" -- this is wrong. You'll need the plural form
of "licenses", or it won't work (this took me some time to discover).
Synopsys has also added a very nice feature that allows you to invoke the
dc_shell along with the required licenses right off the bat. The
combination of these two features allow the designers to get the dc_shell
with the needed licenses and then give up the (V)HDL reader right before
the mapping stage of the compile.
It is very nice to see a vendor respond to the cries of the users, even if
it does take a few years.
There is a snag, however - if you want to use "compile -scan" then a "Test
Compiler" license is checked out and is kept during the entire optimization
stage. And, I have not found a "test_keep_license=false" variable - and
I've tried.
- Victor J. Duvanenko
Truevision
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