How can I change configuration via package constant?

Hello,

I have a problem, a style probem.

In my design, some blocks might switch from a more performing and more resource consumming architecture to a less performing and less occupying one.

Which architecture will win is still to be decided.

I wish I could switch between those architectures by changing the value of a constant in a global package and having it work in the configuration section of the top level architecture.

Something like:

configuration CFG_TOP of TOP_FILE is

for schematic

for I_1,I_2: code_1

use configuration slow_cfg when global_switch='1' else

use configuration fast_cfg;

end for;

end for;

end CFG_TOP;

Should this global package constant work, I could switch several blocks from architecture to architecture at the same time, having not to worry for forgetting a code.

Can anybody help me to solve this problem?

Thank you,

Simona.