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Forums > Digital IC > Floorplanning, Place and route

Subject: About Encounter Warning 'TA-549'
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eminemshow
Posts: 75
Online: User is Offline
2/26/2008 6:55 PM  
hi All:

I get the following message when run timing analysis:

--> WARNING: Pin 'msd_ddr_phy/ddr_sstl/dll_ato_io125/AE' is driven 'ZERO' and
             'X' simultaneously, preserving 'X.' .
--> WARNING: Pin 'msd_ddr_phy/ddr_sstl/dll_dto_0_io121/OJ' is driven 'ZERO' and
             'X' simultaneously, preserving 'X.' .


Why? Does it relate to constant propagation? where comes the 'X'?
ejm
Posts: 8
Online: User is Offline
3/27/2008 3:14 PM  
If there a different drivers on a net, and they are not driving the same signal state (0,1,X) on to the
net, then system has to resolve which state the signal is in in order to propagate forward.

The Warning you see indicates that there is such a conflict - in the case between a X (unknown) state and 0 (ZERO)
state. The timer resolves this "conservatively" by keeping the X. All signals have a state value of X in the timer
unless some explicit state assertion is made (set_case_analysis), and propagated forward.

Other tools (PT I think) resolve the above scenario to ZERO rather than X. There is a CTE global to provide a similar
resolution policy:

set_global timing_resolve_driver_conflicts {conservative | aggressive}

default: conservative

(Note: for some reason this global is not in the current doc set. We'll look into getting that added)
eminemshow
Posts: 75
Online: User is Offline
3/27/2008 7:40 PM  
Many thanks. EJM!

If there is a X state, what does this stand for? Does X means '0' or '1'? Or X means 'high resistance state'?
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Forums > Digital IC > Floorplanning, Place and route > About Encounter Warning 'TA-549'


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