what are clockgating paths

[huckle189]

Newbie question:

What are clockgating enable paths? Are these real or false? Can you explain with example?

Thanks,

 

[rca]

clock gating enable is a signal to stop the clock propagation, so basicly, if you used a AND gate with one input connected to the clock and the second input connected to this clock enable, you will stop the clock (not the cleanest way)

 

[cheryl0216]

When u do primetime, you can use set case analysis to test the path sometime.

 

[softguru]

Clock gating cells(ICG) are basically a negedge latch plus AND gate. Lets say "enable" is the signal used to gate the clock "clk". Then the "enable" signal will latched by the ICG on "clk"'s negative edge. If enable has changed from 1 to 0 on the posedge of "clk", then ICG would have latched '0' on the negedge of "clk" (i.e. half clock shifted). Output of this latch will be used by the AND gate to stop the "clk". This makes sure that there is no glitch on the gated clock.

Now path from the flops where "enable" is generated till the "EN" port of the ICG cell is the "clock gating path". Note "enable" will be typically generated from "clk"'s posedge. So this timing path will be "half cycle path". This is a true path and should be met.

 

[dftrtl]

paths on to clock gating cell are real.