Performing Readback from Impact

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I am trying to perform a readback (for the first time) from ISE
(impact) on my Virtex II device. For some reason that feature is not
enabled (even after I enabled readback feature while programming it.)

I tried finding docs which discuss this, but failed. I did find some
resources on how to readback (but not from ISE). I never got a reply
from Xilinx Customer service when I filed a webcase!

It would be great if someone can help me.

Thanks.


Re: Performing Readback from Impact
Praveen,

Readback of FPGAs using iMPACT is not supported - never has been :-(.
You can, however, do a "verify" in which the contents of the FPGA is
compared against the source bitstream file.

Praveen wrote:
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Re: Performing Readback from Impact
Thanks Glenn. Why list that option when we can't use it? ;). I read in
the Impact help file that it can be used when using desktop
configuration mode. But, I read elsewhere (in Xilinx help file) that
suggested it can be used in SMAP and JTAG config modes. Doesn't make
any sense.


Re: Performing Readback from Impact
Praveen,

The readback operation is supported in iMPACT only for PROMs and CPLDs
in Boundary-Scan and Desktop modes.  Since iMPACT is a generic Xilinx
device configuration tool it indicates the complete set of operations
available for ALL devices but disables the ones that are not supported
for the selected device.

This is not unusual.  For instance, in "Word" you may not be able to Cut
or Paste a protected document yet the operation is visible but disabled.


Praveen wrote:
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Re: Performing Readback from Impact
Hi Neil,

I think what you say is not entirely correct - impact doesnt do FPGA
readback, not because it can not support it because Xilinx decided not to
include this feature (available to the user).

doing verify with FPGA in iMpact actually DOES readback of FPGA into
internal buffer, then compares it to the .BIT file using the .MSK file and
then trashes the internal readback. So the FPGA readback is internally used
by impact, just the readback can not be saved to a file.

sure the readback would not be the same as the programmed bitstream if the
FPGA has been started, eg you would only get the proper .bit being read if
the readback is done after JTAG configuration, but before jstart
instruction, which I agree would be very rare case indeed. So I kind of
understand why the FPGA readback is 'left out' from impact, but it doesnt
mean its not possible. the usefullness of the readback is sure a question,
there are only a few cases where it could be useful.

Antti


"Neil Glenn Jacobson" <n.e.i.l.j.a.c.o.b.s.o.n.a.t.x.i.l.i.n.x.c.o.m.>
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Re: Performing Readback from Impact
Antti,

I didn't say it was impossible.  I said it wasn't supported :-)


Antti Lukats wrote:
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