What is TBuf?. Implementation error - excess use of TBuf!

[xtcx]

Hello guys!, I'm using Spartan3 2000 k FPGA from Xilinx and using 8.2i ISE version. Well!. comming to the point. I added some enumerated data type with attribute property like this
------------------------------------
Signal timer : integer :=0;
TYPE timer is (start, timeout, stop);
signal radio_timer : stop;
Attribute init : string;
Attribute init of radio_timer : signal is "stop";
Attribute init of timer : signal is "1";
.
.
.
.
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Next to this, I added a small counter logic which resets the unit if the input has not arrived within the specified time....Now when I ran synthesis, it showed "Excess Device utilzation" for component
TBuf : 1 Out of 0
Now this is the first time I'm getting this error, and please tell me what this Tbuf is?. Is it Tristate Buffer?...And I wonder where am I using this Tbuf in my coding?. Those are the only signals I recently defined which caused the error!..Also it says (1/0) which means there is no Tbuf in Spartan3 or what?...It'd be nice of you guys if you could clarify what this Tbuf is and why Spartan 3 doesnt have such...!
Thanks in advance friends!......

 

[dmk]

I am not sure, but the synthesized circuit probably will include some multiplexers, which could be implemented combinationally or by using tristate buffers. So, you should have a look at the Language Templates.

 

[xtcx]

Re: What is TBuf?. Implementation error - excess use of TBuf

Actual tristate buffer means a buffer with anable control. Well, Doesn't xilinx fpga have atleast one?...

 

[dmk]

Yes, they have. That's why in your case the ISE will use 3-state buffers. To avoid this you must look at the Language templates and use Xilinx recommendations how to realize multiplexers inside that kind of FPGAs.