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

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

Hakon, > > How about an OR gate of the status bits indicating a failure to a flip > flop that genreates a one clock long reset pulse? > > Lots of logic? three gates and a FF or two? > > The 'Auto-Lock' suggestion is a good one. We will keep that in mind. > > Austin
Reply to
Håkon Lislebø
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Håkon,

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.

Aust> Hi Austin,

Reply to
Austin Lesea

Håkon,

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,

Aust> Yes I use a 2V40 in that application (155Mb clock data switch/mux), and I

Reply to
Austin Lesea

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