How to use RLOC_ORIGIN

[graffitici]

Hi,

I grouped several LUTs in my design into an RLOC, and put them in a U_SET with the following line in the VHDL file

attribute U_SET of sliceup_i: label is "SWITCH_CHAIN";

Now I would like to position the whole group using absolute positioning on the FPGA (Virtex-II Pro). I tried to do it using the following line in the UCF file:

SET SWITCH_CHAIN RLOC_ORIGIN = "X49Y0" ;

Although this line does what I intend it to do (I can see the circuit in place using the FPGA editor), it does signal an error :

ERROR:ConstraintSystem - In file: combined.ucf(5): 'SET' is not a valid
design object type to associate constraints with.

What is the proper way of setting the RLOC_ORIGIN of a U_SET from within the UCF file?

Thanks,
Berk