Re: [partial-reconfig] Modules and Bus macro

["Umar Mushtaq" <misfit_05@xxxxxxxxxxx>]

Hi...

Can't say much about the first problem, apart from making sure that
you're not missing out on any constraints that you need to apply...
someone submitted a script for unrouting a particular net in
FPGA_Editor... you might want to look at the archives for it, but I
don't know if that is the solution to your problem... 

As far as the control lines for the BMs are concerned, the idea about
using LUTs to control them occured to me too... however, Gregory
Mermoud's tutorial ( look in the archived posts for this month )
suggests that this doesn't work... another option was to use VCCs and
GNDs to control them, but I came across something in the Xilinx website
that said that doing this would not really be good for the device... I
can't find the page on the 'site, but here's what it said:

"Due to the unique circuitry of the FPGA architecture for VCCs,
constants should not be driven from VCC or GND sites in a reconfigurable
module to correctly retain their values during active partial
reconfiguration. The ideal way to drive constant values in a
reconfigurable module is to use LUT sources. Recent versions of the ISE
software do this automatically with the use of the following
constraints: 

ISE 5.x: 
AREA_GROUP "AG_reconfig" ROUTE_AREA = RECONFIG
DISALLOW_BOUNDARY_CROSSING RECONFIG_MODE; 

ISE 6.x: 
AREA_GROUP "AG_reconfig" MODE=RECONFIG; 

If you are using an older software version, a LUT can be instantiated
for use as a constant source. To verify that your constant signals have
been implemented correctly, verify that no VCC or GND sites are included
in your reconfigurable module through the use of FPGA Editor. "

However, the tutorial I mentioned above suggests that using LUTs doesn't
really work in practice, even if Xilinx suggests it does...

So that means we're left with using external lines concatenated into
control signals for the BMs... For a long time I kept wondering why the
xapp290 design used external lines when the BMs could so easily be
controlled by using constants, either by entering 0s and 1s as you
suggest, or by feeding the values to the top level from a module...
obviously they've done so for a reason... It would therefore be a good
idea to use external lines in the manner xapp290 uses... besides there's
no real loss of I/O ports, since for a three module design you need only
four external lines...

I hope this helped...

Sincerely,
Umar
-- 
  Umar Mushtaq
  misfit_05@fastmail.fm

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