Vision VHD-800 Dokumentacja Pobierz pdf (Strona 14)

Student Task 6: Using the report_timing command determine the timing information of the circuit. Which of the

timings illustrated in Figure 7 gets actually reported?

Which timing gets reported if you do not specify a clock constraint (i.e. the timing information gathered in Section 6.1)?

The four different timing paths of Figure 7 shall be investigated in the datapath.vhd circuit. Therefore, we need better

speciﬁed timing reports. In order to be able to report speciﬁc timing paths, we have to specify the start and/or end points

of the paths.

A meaningful starting point of a path is the input of our circuit (for t

and t

) or the clock input of a ﬂip-ﬂop (for t

and t

Similarly, the end points for a timing path are either circuit outputs (for t

and t

) or the input pin of a ﬂip-ﬂop (for t

and

Fortunately, it is easy to identify the inputs, outputs, and ﬂip-ﬂops within our netlist. This is because the SYNOPSYS DESIGN

COMPILER provides the commands all_registers, all_inputs and all_outputs. Furthermore, the command

report_cell can be used in order to report detailed information about logic cells. Registers will be named by the

SYNOPSYS DESIGN COMPILER by appending a “ reg” to the signal names. For example, a cell named DataxDP reg[14] is

certainly a ﬂip-ﬂop. Flip-ﬂop clock pins are labeled with a CK .

Student Task 7: Use the commands all_registers, all_inputs, all_outputs, and report_cell to extract

speciﬁc cell information:

• Find all ﬂip-ﬂops and write down their names here:

• What is the name and the width of the data input?

Name = Width =

• What is the name of the clock input?

Now, we have to combine the previously mentioned commands with the report_timing command in order to get all the

timing information illustrated in Figure 7 of our design. The start and the end points, which should be taken into consider-

ation when using the report_timing command, can be determined using the arguments -from and -to, respectively. In

the following, an example printing the t

timing is given:

dcs > report_timing -from [all_inputs] -to [all_registers -data_pins]

Student Task 8: By combining the report_timing command with the all_registers, all_inputs, and

all_outputs commands, complete the following timing information together with their respective slack:

= t

slack

= slack

What is the maximum clock frequency? Which one of the t

timing parameters dictates it?

max

You are done with the ﬁrst part of Exercise 3. Discuss your results with an assistant.

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Vision VHD-800 Dokumentacja Strona 14