Howto disable Quartus infering M4Ks??

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I have some problems with a design I am porting from Xilinx to Altera.
The fitter dies with a message about the design not fitting into the
device.Further investiogation shows that Quartus tries to move a lot
of small shiftregisters (32-bit x 4) into M4Ks, which is a not the
best use of my embedded memories...

Can anyone explain to me why this happens? I am using 75% of the FPGA
right now and should be able to get the small shift registers into
LEs. Is there any way to let Quartus infer none or _some_ of the shift
registers into M4Ks and use LEs for the rest??


(I am using Quartus Webpack version 8.0, build 231 07/10/2008)

thanks for any help

Re: Howto disable Quartus infering M4Ks??
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Try running quartus with no constraints other than
the device family.

        -- Mike Treseler

Re: Howto disable Quartus infering M4Ks??
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In the Quartus UI use the Assignments menu as folows : Assiginmnets-
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in the dialog t a set of Maximum Setting entries which look like
Maximm Number of M512 memory blocks. Set it to 0 or any non zero
number other than -1 (which is default).

Hope tis helps,
Subroto Datta
Altera Corp.

Re: Howto disable Quartus infering M4Ks??

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M512's or M4k's?  Or to make it use M512's instead of M4k's?

Re: Howto disable Quartus infering M4Ks??

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There are separate settings for both, and -1 means unlimited.
But I don't think this will help.

The OP said

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I expect that quartus was out of LEs
on the specified device,
and the excess shifters did
not match the available blockram.

The quickest way to test this theory
is to spec a larger device.

If this fails I would either break up the design,
revert to version 7.2, or open a case with Altera.


       -- Mike Treseler

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