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16th March 2019, 00:23 #21
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16th March 2019, 01:03 #22
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Re: minimum depth for data streaming through async fifo
This post #3 does not say the clocks are frequency locked
It says they are equal in frequency (a vague description of clocks if you ask me).
Clocks in many systems maybe the same nominal frequency, but are NOT locked to each other and therefore exhibit an absolute difference in their frequencies that can result in phase drift between the two clocks. There are no 0 PPM clock sources.
Unless you specifically state that the clocks are PHASE and/or FREQUENCY locked we can be sure if they are or not, hence all the questions and assumptions made.
If they are frequency locked you might not even need a FIFO (depends on why there is a phase difference) and can treat it as a synchronous transfer.

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16th March 2019, 01:32 #23
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Re: minimum depth for data streaming through async fifo
3. the two clks are frequency clocked but they are considered async to each other.
This #3 is mentioned in another post.
You should take the description as is. When I said equal, this should imply that their frequencies are absolutely the same. Why would you go assume they are not, though it may not be practical?

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Yesterday, 15:55 #24

Yesterday, 16:40 #25
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Re: minimum depth for data streaming through async fifo
Hi,
even "locked" clock signals will move.
But how much?
It depends on
* the stability of the input clock
* the division and multiplication factors (if analog PLL)
* the lock mode
* the feedback filter
* the VCO stability
I won´t be surprised if it will move more than "several x 360°" (several output full waves). Yes, in "locked" state!
(high division factor, high multiplication factor, unstable input)
... because the phase comparator just sees the divided phase.
With a multiplication factor of 1000 (for example) the phase comparator just sees 0.36° when the output clock is shifted by 360°....
But how can we know?
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.
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