09-14-2010 07:31 AM
I have a signal that is created from the XORing of two signals, Data Strobe decoding for the clock. Then I take that signal
and run it into a BUFG. This signal is fed into a Hierachical Block where the input name of the block is different than
the clock signal coming out of the BUFG.
I am looking in the Constraints editor for the signal name so I can constain the clock period of the derived clock signal but I can not find it in the list of clocks in the constraint editor.
Is there a attribute I can put in VHDL modules that will define the derived signal as a clock.
09-14-2010 07:53 AM
If the signal drives the clock pins of DFF in IOB or CLB, then it is a clock (it is implicit in what it gets wired to).
I would look in FPGA_Editor, and find the name of the clock net, as you will need a PERIOD constraint on this clock to allow the tools to know what to do about the timing.
09-14-2010 08:20 AM
09-14-2010 08:46 AM - edited 09-14-2010 08:47 AM
Thank You Austin,
I looked at the RTL Schematic and I can see the name of the signal there. I will try to constrain the signal (clk)
and see if it works. The title of the message should have said defining a internal signal as a clock signal.
09-14-2010 10:49 AM
I tried using my net name in my case, GLOBAL_CAM_DS_CLK.
It could not find the signal eventhough I saw this name in the FPGA Editor.
So I tried using the Timing Analyzer and created a Report on Clock Regions in the report it showed the following
Now I tried to use these statements:
NET "CAM_IF_TP/CAM_INPUT_PATH1/GLOBAL_CAM_DS_CLK" TNM_NET = CAM_IF_TP/CAM_INPUT_PATH1/GLOBAL_CAM_DS_CLK;
TIMESPEC TS_GLOBAL_CAM_DS_CLK = PERIOD "GLOBAL_CAM_DS_CLK" 20 ns HIGH 50%;
To me it looks like internally generated clocks use a more complicated name. If I used just the
name GLOBAL_CAM_DS_CLK it will not find the Net.
It is now appearing on the synthesis report as CAM_IF_TP/CAM_INPUT_PATH1/GLOBAL_CAM_DS_CLK