how to check setup and hold-time between mixed positive and negative edge trigger FF

[liwei039]

1.How can I check the setup time and hold time for a timing path. the first FF is positive edge trigger, but the end FF is negative edge trigger one.
2. The hold time is still depended by clock frequency like normal?

Thanks

 

[shitansh]

If a design has both negative-edge triggered flip-flops (active clock edge is falling edge) and positive-edge triggered flip-flops (active clock edge is rising edge), it is likely that half-cycle paths exist in the design. A half-cycle path could be from a rising edge flip-flop to a falling edge flip-flop, or vice versa. Figure 8-19 shows an example when the launch is on the falling edge of the clock of flip-flop UFF5, and the capture is on the rising edge of the clock of flip-flop UFF3.

 

[liwei039]

Hi, shitansh,

Thanks, so in this case, the hold time check is dependent on clk freq? right?
Can you give me the equations for setup and hold time check?

 

[pavanks]

Hi the timing tool will recognise and do the required anlysis and comes up with the slack value.
But if there is a positive clock triggered flop at the launch and a neg clock triggered at the capture flop using the same clock, then there is only half cycle left for the setup and hold also gets half cycle.
So ur hold will have a good margin but ur faced with many setup violations.

Hope its clear....