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

t...@gmail.com wrote:
> 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...

Try running quartus with no constraints other than
the device family.

        -- Mike Treseler

On Jul 19, 2:13=A0am, tgau3...@gmail.com wrote:
> 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

In the Quartus UI use the Assignments menu as folows : Assiginmnets-
>Settings->Analysis & Synthesis Settings->More Settings . Scroll down
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.

On Jul 19, 10:33 am, Subroto Datta
<sda...@altera.com> wrote:

> > 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...

> 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).

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

c...@hotmail.com wrote:

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

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

The OP said

> The fitter dies with a message about the design not fitting
> into the device.
> I am using Quartus Webpack version 8.0, build 231 07/10/2008

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

What mr Datta suggested did not work but
eventually got me on the
right track. From the same location in the Settings, I disabled
automatic inferring of RAM and shift registers. Then I re-wrote the
design to specifially use embedded memory where it was needed. This
seem to solve the problem and also leaves 2.5K LUTs free after full
synthesis.

I think the problem was that Quartus used an all-or-nothing approach
during mapping. It took my ~70 shiftregisters and made it into one
giant shiftregister, then tried to fit all of them either into LUTs or
RAMs.

thanks everyone for your help!