Max Tpd of a LUT -> calculation of a maximum number of the LUTs allowed between two flops.

Hello,

I'd like to create a thumb rule about how many LUTs I would allow between two flops when I synthesize a module as a stand alone module.

I thought about a thumb rule of giving 50% of the timing budget to logic elements and 50% for route.

In order to know how many logic elements (LUTs) I would allow between two flops, I need to know a Tpd of a LUT (worst path).

So, the formula should be simple:

Max # of LUTs between flops = (1/Freq) * 0.5 / (Tpd of LUT)

So, anyway, where can I see the timing parameters of the LUT and other logic elements in the device?