Re: Logic minimization software with LUT6 sup****t?

<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