John_H wrote:
> <dudesinmexico@[EMAIL PROTECTED]
> wrote in message
> news:1190849356.286625.69510@[EMAIL PROTECTED]
>
>>Ray, nice to hear from you. Yes, I have considered BRAMs as lookup
>>tables.
>>In fact, we noticed that Synplify does something pretty cool: it packs
>>two multipliers
>>in a single BRAM18, using one ****t for each multiplier. Of course this
>>is possible since
>>they share the same table.
>>According to the do***entation, one can use a BRAM36 as two BRAM18s,
>>however
>>PlanAhead refuses to place a pblock with two BRAM18s on any area with
>>just one BRAM36.
>>This could be either a PlanAhead bug or simply that the BRAM36 still
>>has just two ****ts...
>
>
> From p 125 of ug190.pdf (v3.1 Virtex-5 User Guide, 9/11/2007)
>
> Two RAMB18s can be placed in the same RAMB36 location by using the
BEL
> UPPER/LOWER constraint:
> inst "my_ramb18" LOC = RAMB36_X0Y0 | BEL = UPPER
> inst "my_ramb18" LOC = RAMB36_X0Y0 | BEL = LOWER
>
> which is echoed in Ansew Record 25115
>
>
http://www.xilinx.com/xlnx/xil_ans_display.jsp?iLanguageID=1&iCountryID=1&getPagePath=25115
>
> though I think the note's author forgot to write UPPER for the last
line.
> Darned cut & paste!
>
> Whether PlanAhead sup****ts these constraints natively isn't obvious.
Ask
> the hotline or your FAE!
>
> - John_H
>
>
Oops, I misread what you were saying here, I thought you were trying to
use the BRAM36 dual ****ted. I don't often use plan ahead. Putting the
bel constraints on instantiated BRAM18's works fine for placing them
together.
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