> Hi Antti,
>
> Antti wrote:
> > I still wish Xilinx FPGAs would have the config Clock accessible again
> > as it was with old Xilinx FPGAs !
>
> A little bit of a late response here, but the STARTUP_VIRTEX5 primitive
> gives you access to both the configuration clock and the internal
> housekeeping clock.
>
> See http://toolbox.xilinx.com/docsan/xilinx82/books/docs/v5ldl/v5ldl.pdf
> for the full usage in HDL.
>
> -m
Thank You Max and Thanks to Xilinx
- I have been jammering about re-gaining the access to configuration
clock for ages, now it has finally come true.
It was there in early Xilinx products, it is there in Altera and
Lattice products, and since Virtex-5 it is again back in Xilinx
products as well. Spartan3A doesnt seem to have it, but lets hope
Spartan4 or upcomig Xilinx non-volatile products will have it in as
standard feature.
Antti
Reply by Max Baker●September 21, 20062006-09-21
Hi Antti,
Antti wrote:
> I still wish Xilinx FPGAs would have the config Clock accessible again
> as it was with old Xilinx FPGAs !
Antti,
As convenient as the PMV is, it is actually 16 different ring
oscillators. We would have to fully characterize all of them in order
to pick the "best" one, and then create a user macro to instantiate it...
Maybe some day, but right now it is not even on a list of "nice to have..."
Austin
Antti wrote:
> Austin Lesea schrieb:
>
>> Antti,
>>
>> The PMV is not used for configuration.
>>
>> In fact, it was not intended to be used by anything at all. It is there
>> for test only.
>>
>> As such, it is uncharacterized. Anything that is uncharacterized can
>> NOT be made available for customer use. The DCM NBTI macro did make use
>> of it, as that macro needed an oscillator for when no clock was present,
>> and the less resource used by a macro, the better the macro (least
>> impact on any design).
>>
>> If you want a ring oscillator, (which is all that the PMV is), you can
>> easily make one out of a chain of LUTs.
>>
>> Austin
>>
>> Antti wrote:
>>> Hi All,
>>>
>>> as I had guessed for long time the PMV primitive is actually the
>>> on-chip oscillator, most likely it is the same oscillator that is used
>>> for configuration. And it can be used from user designs as well. PMV is
>>> present in all recent FPGAs.
>>>
>>> http://xilant.com/index.php?option=com_content&task=view&id=29&Itemid=32
>>>
>>> When I opened webcase about the issue that Xilinx tools made fatal
>>> failure when I tried to use the PMV from an hard macro the response was
>>> that, "you dont need to know" - well now I know :)
>>>
>>> Antti
>>>
>
> Hi Austin,
>
> hmm, well the PMV sounds like better oscillator than the chain of LUT's
> as it always in the same place and doesnt need LOC constraints etc? The
> PMV looks like a available replacement for the actual config clock
> primitive.
>
> I still wish Xilinx FPGAs would have the config Clock accessible again
> as it was with old Xilinx FPGAs !
>
> Antti
>
Reply by Antti●August 30, 20062006-08-30
Austin Lesea schrieb:
> Antti,
>
> The PMV is not used for configuration.
>
> In fact, it was not intended to be used by anything at all. It is there
> for test only.
>
> As such, it is uncharacterized. Anything that is uncharacterized can
> NOT be made available for customer use. The DCM NBTI macro did make use
> of it, as that macro needed an oscillator for when no clock was present,
> and the less resource used by a macro, the better the macro (least
> impact on any design).
>
> If you want a ring oscillator, (which is all that the PMV is), you can
> easily make one out of a chain of LUTs.
>
> Austin
>
> Antti wrote:
> > Hi All,
> >
> > as I had guessed for long time the PMV primitive is actually the
> > on-chip oscillator, most likely it is the same oscillator that is used
> > for configuration. And it can be used from user designs as well. PMV is
> > present in all recent FPGAs.
> >
> > http://xilant.com/index.php?option=com_content&task=view&id=29&Itemid=32
> >
> > When I opened webcase about the issue that Xilinx tools made fatal
> > failure when I tried to use the PMV from an hard macro the response was
> > that, "you dont need to know" - well now I know :)
> >
> > Antti
> >
Hi Austin,
hmm, well the PMV sounds like better oscillator than the chain of LUT's
as it always in the same place and doesnt need LOC constraints etc? The
PMV looks like a available replacement for the actual config clock
primitive.
I still wish Xilinx FPGAs would have the config Clock accessible again
as it was with old Xilinx FPGAs !
Antti
Reply by Austin Lesea●August 30, 20062006-08-30
Antti,
The PMV is not used for configuration.
In fact, it was not intended to be used by anything at all. It is there
for test only.
As such, it is uncharacterized. Anything that is uncharacterized can
NOT be made available for customer use. The DCM NBTI macro did make use
of it, as that macro needed an oscillator for when no clock was present,
and the less resource used by a macro, the better the macro (least
impact on any design).
If you want a ring oscillator, (which is all that the PMV is), you can
easily make one out of a chain of LUTs.
Austin
Antti wrote:
> Hi All,
>
> as I had guessed for long time the PMV primitive is actually the
> on-chip oscillator, most likely it is the same oscillator that is used
> for configuration. And it can be used from user designs as well. PMV is
> present in all recent FPGAs.
>
> http://xilant.com/index.php?option=com_content&task=view&id=29&Itemid=32
>
> When I opened webcase about the issue that Xilinx tools made fatal
> failure when I tried to use the PMV from an hard macro the response was
> that, "you dont need to know" - well now I know :)
>
> Antti
>
Reply by Antti●August 30, 20062006-08-30
Frank Buss schrieb:
> Antti wrote:
>
> > When I opened webcase about the issue that Xilinx tools made fatal
> > failure when I tried to use the PMV from an hard macro the response was
> > that, "you dont need to know" - well now I know :)
>
> Ok, but when you create a schematic with a FPGA, which uses this
> undocumented feature and you produce some million parts, but Xilinx decide
> to cancel it in later revisions of the FPGA, you are lost.
>
> --
> Frank Buss, fb@frank-buss.de
> http://www.frank-buss.de,http://www.it4-systems.de
sure - care should be taken when making any decisions. well currently
it *IS* used by all Virtex-4 silicon, as the Xilinx tools use it for
every design you make, you are just not seeing it. it is added
silently, only visible in FPGA editor. so as long as the new Virtex-4
steppings are bitstream backward compatible the PMV feature will be
there as well.
its just the configuration clock primitive - that is for some reasons
made unaccessible (or not easily) accessible for the FPGA users.
Antti
Reply by Frank Buss●August 30, 20062006-08-30
Antti wrote:
> When I opened webcase about the issue that Xilinx tools made fatal
> failure when I tried to use the PMV from an hard macro the response was
> that, "you dont need to know" - well now I know :)
Ok, but when you create a schematic with a FPGA, which uses this
undocumented feature and you produce some million parts, but Xilinx decide
to cancel it in later revisions of the FPGA, you are lost.
--
Frank Buss, fb@frank-buss.de
http://www.frank-buss.de,http://www.it4-systems.de
Reply by Antti●August 30, 20062006-08-30
Hi All,
as I had guessed for long time the PMV primitive is actually the
on-chip oscillator, most likely it is the same oscillator that is used
for configuration. And it can be used from user designs as well. PMV is
present in all recent FPGAs.
http://xilant.com/index.php?option=com_content&task=view&id=29&Itemid=32
When I opened webcase about the issue that Xilinx tools made fatal
failure when I tried to use the PMV from an hard macro the response was
that, "you dont need to know" - well now I know :)
Antti