Re: Why can't Xilinx DCM's regain lock without a RESET??

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Hi Austin,

Yes, you could make an edge detect which generates a reset pulse. I tried
it. But if the clock is lost the reset pulse will go away long before the
clock is back and then the DCM needs another reset. That reset will off
course come when CLK_LOS goes off, but I can not trust the CLK_LOS because
the open clk input picks up signal from another clock (BLVDS) and will often
indicate that a clock is present. An auto reset for my applications take som
FF's (shift register, delay to wait for lock signal after reset) and gates.
Multiply that with four DCM's and suddenly a small Virtex-II is gotten even
smaller. Off course you cannot cover all situations, and my telecom
application is a little bit demanding. It is just that an Auto-Lock would
have fit in so nicely!  Yes, squeese that feature into the next  -
Virtex-III?

Hakon


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Re: Why can't Xilinx DCM's regain lock without a RESET??
Hkon,

Well, sounds like you really do have a demanding application, and it therefore
it needs a well thought out and debugged solution.  I would hate to try to match
our system design skills with yours (and get it wrong) so the cheapest and best
way to address thius is still using LUTs, SRL16s, and FFs.

And what are you using, a 2V40?  We are still talking about less than a few
hundred CLB's, which is a tiny number in a 2V1000 or larger.  If it is a 2V40,
or a 2V80, I can see your point, as it might get a bit crowded.

Is it possible to multiplex your clock quality logic among multiple DCMs?  Sort
of a reset controller?  Or use a picoBlaze to control all DCM resets?  It is not
a function that needs the speed of the fabric, so one can replace it with
software, and a soft controller core like the picoBlaze.  Might be an
advantageos trade-off.

Austin

"Hkon Lisleb" wrote:

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Re: Why can't Xilinx DCM's regain lock without a RESET??
Hkon,

You are welcome.  It is wonderful to hear from folks who are doing what I used
to do for 23 years (design telecoms equipment) and using the parts I helped
design.  It is your feedback that leads to future feature enhancements,

Austin

"Hkon Lisleb" wrote:

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