Input to Synchronizer/Metastability chain

There's two components to the synchronizer:

1) The path from a register in one domain to the first register in the other domain. This is asynchronous and the user should cut timing on it. (I suggest cutting timng between the domains with set_clock_groups). This path should have no affect on MTBF and not be analyzed.

2) The next part are is the path to the second register(and if there are more synchronization stages, the path to each). These are all in on the same clock domain, should be analyzed by TimeQuest as a pass/fail on whether it met timing, and then analyzed for MTBF based on how much positive slack. As you mention, if the slack is negative there is no MTBF, as it will always fail.

Anyway, the asynchronous path and the synchronizer should be two separate things.

Out of curiosity, how do you like the MTBF analysis? I don't see this used very much although think it's a very cool tool. (My feel with metastability is that it's generally easy to fix if you have a way to identify and analyze it. Most tools don't do this, while TimeQuest actually does a very good job.)

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There's two components to the synchronizer:

1) The path from a register in one domain to the first register in the other domain. This is asynchronous and the user should cut timing on it. (I suggest cutting timng between the domains with set_clock_groups). This path should have no affect on MTBF and not be analyzed.

2) The next part are is the path to the second register(and if there are more synchronization stages, the path to each). These are all in on the same clock domain, should be analyzed by TimeQuest as a pass/fail on whether it met timing, and then analyzed for MTBF based on how much positive slack. As you mention, if the slack is negative there is no MTBF, as it will always fail.

Anyway, the asynchronous path and the synchronizer should be two separate things.

Out of curiosity, how do you like the MTBF analysis? I don't see this used very much although think it's a very cool tool. (My feel with metastability is that it's generally easy to fix if you have a way to identify and analyze it. Most tools don't do this, while TimeQuest actually does a very good job.)

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Thank you! I tried to "set_clock_groups" within the Time Quest GUI, but the node finder only allowed me to search with the command "get_clocks" which only revealed the PLL clocks.

I closed the node finder and typed in "get_ports" with the external clock port name and it rejected my command because i used "get_ports" instead of "get_clocks". I also just tried just typing the name of my 125MHz clock in the GUI and it looks like it tries to run the "get_clocks" command on whatever I typed in the box. This again rejects the command because it does not recognize my external clock with the "get_clocks" command.

I did verify my "get_ports" and "get_keepers" command from the View->Name Finder tool.

When I report my clocks it recognizes my external 125MHz clock and that it is of "Base" type.

Should I be defining my external 125MHz clock a different way?

Here is my printout of warning messages:

Warning: Ignored assignment: set_clock_groups -exclusive -group [get_clocks {inst|altpll_component|auto_generated|pll1|clk[0]}] -group [get_ports {clkout_dsp}]

Warning: Collection filter Argument -group with value [get_ports {clkout_dsp}] requires type ( clk ), but found type port.

and for the time when i just tried typing in the name of my 125MHz external clock in the GUI it said this:

Warning: Ignored assignment: set_clock_groups -exclusive -group [get_clocks {clkout_dsp}] -group [get_clocks {inst|altpll_component|auto_generated|pll1|clk[0]}]

Warning: Argument -group with value clkout_dsp could not match any element of the following types: ( clk )

As for using the MTBF I have not really used it myself, but i do like that it's there. I was only playing around with it when trying to get my timing violation to go away.

oops, I did not have the "Case Insensitive" box checked off when using the Clock Group GUI.

I was able to successfully generate the clock groups and looks like that solved my timing complaint!

Thank you, you've helped me out greatly and now I know a little bit more about the power of Time Quest!