Xilinx Answer #3909 : M1.4: WARNING:basts:75 - TPTHRU "IBUS_PATH" is on NET "IBUS2", which is notconnected to any drivers.

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M1.4: WARNING:basts:75 - TPTHRU "IBUS_PATH" is on NET "IBUS2", which is notconnected to any drivers.

Record #3909
Problem Title:
M1.4: WARNING:basts:75 - TPTHRU "IBUS_PATH" is on NET "IBUS2", which is notconnected to any drivers.

Problem Description:
Urgency: Standard

General Description:
In this design, the TPTHRU is used to create a slow exception
off FROM:TO constraint.

The design is as follows:

input ----->ff1 ------->BUFE-------->ff2----->output
             |
              ----------------->ff2

NET IBUS2 is between output of bufe and ff2.
The following constraints are in ucf:
NET IBUS2 TPTHRU = IBUS_PATH;
TIMESPEC TS_TIG = FROM:FF1:THRU:IBUS_PATH:TO:FF2:TIG;
TIMESPEC TS01 = FROM:FF1:TO:FF2:10;

ngdbuild give the following warnings:
WARNING:basts:75 - TPTHRU "IBUS_PATH" is on NET "IBUS2", which
is not connected to any drivers.
WARNING:basts:16 - TPTHRU TIMEGRP "IBUS_PATH" has been applied
only toINST, PIN, or NET elements that are not connected to
the rest of the design. This occurs if a TPSYNC is placed on
a macro that is empty, a block that has no
input pins that are driven by a net, an undriven macro pin,
an output pin that does not drive anything, or a net that is
not driven. Please correct this situation.

Solution 1:

The THRU get pushed to all drivers on the TBUF net at the top
level of the design hierarchy, but not those drivers at a lower
hierarchy level.

This problem is fixed in M1.5.

Some workarounds for M1.4 :
1. Use a different TNM for the Flops driven by the bufe.
    If you do this you can get around the problem by just
    specifying from:to timespec.

2. Use the following constraint:
    PIN $1I58/$1I10.O TPTHRU = IBUF_PATH;
    **$1I58 is the name of BUFE instantiation,
       $1I10 is the name of BUFT instantiation inside
       the BUFE macro, and O is the output pin.

3. Use buft with inverted t input on toplevel to replace
    bufe symbol.

End of Record #3909 - Last Modified: 04/05/99 14:54

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