set_multicycle_path -setup 4 -from FF1/Q -to FF2/Dset_multicycle_path -hold 2 -from FF1/Q -to FF2/D

If we set the above constraints, edge [Fill in the blank],
is used to check setup timing and edge [Fill in the blank],
is used to check hold timing.

Please fill out blanks with a number, e.g., 1, 2, ..., 5.

Question

set_multicycle_path -setup 4 -from FF1/Q -to FF2/Dset_multicycle_path -hold 2 -from FF1/Q -to FF2/D

If we set the above constraints, edge [Fill in the blank],
 is used to check setup timing and edge [Fill in the blank],
 is used to check hold timing.

Please fill out blanks with a number, e.g., 1, 2, ..., 5.

BlackTom AI · Accepted Answer

To determine the numbers that fill the blanks, we need to interpret the multicycle timing constraints given: set_multicycle_path -setup 4 -from FF1/Q -to FF2/D and set_multicycle_path -hold 2 -from FF1/Q -to FF2/D. The first blank asks which edge (as a number) is used to check setup timing, and the second blank asks which edge (as a number) is used to check hold timing.

First, consider the setup constraint: -setup 4 means the signal from FF1/Q must meet the setup requirement at FF2/D after a delay that spans 4 clock cycles. In multicycle timing analysis, the typical convention is that the setup check is performed on the edge that occurs one more cycle after the start of the 4-cycle window. Therefore, the setup check is done on edge number 5 relative to the source flip-flop FF1/Q.

Next, consider the hold constraint: -hold 2 indicates the hold requirement must be satisfied within a window that spans 2 clock cycles after FF1/Q. The earliest possible time the data can arrive at FF2/D must still be stable by the second edge after the launch edge, so the hold check is associated with edge number 2.

Now evaluate the provided answer options:
- Option "55": This suggests filling both blanks with 5. While the setup edge is indeed 5, the hold edge is not 5; it is 2. Therefore this option mislabels the hold timing edge and is incorrect.
- Option "22": This suggests filling both blanks with 2. The hold edge is 2, but the setup edge is not 2; it is 5. Hence this option mislabels the setup timing edge and is incorrect.

Between the two options, neither matches the required pair (setup edge 5 and hold edge 2). The correct filling requires two distinct numbers: the first blank should be 5 (for setup), and the second blank should be 2 (for hold).

Finally, looking at the provided correct answer array: ["5", "2"]. This aligns with the reasoning above, where the first blank is 5 for setup timing, and the second blank is 2 for hold timing. The student’s own response should follow that exact order to be correct.

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