Motivation for learning timequest with black gold (3)

Unconsciously, I learned chapter 4. However, the complete analysis of the internal and external models of TQ is still not well understood. Next, learn .........

 

We also understand the first step of static timing analysis, namely the clock constraints. In addition, I also learned a little more about report timing, how to list relevant time series reports in one fell swoop.

Here we need to use the set_multicycle_path constraint command.

Strictly speaking, the binding behavior of set_multicycle_path tells timequest to update the startup and lock edges of a certain node... surely readers cannot understand it, right? To be a dummies, tell timequest that a pair of nodes may not work in one clock cycle.

I am not intentionally confused. Here I just want to prove one thing. The function of set multicycle path is to tell timequest that "a certain pair of nodes work with N clocks ". However, it can not only target "all nodes", but also "Single-to-node ". In addition, I would like to remind you of one thing... at best, the set multicycle path tells "a pair of nodes work with N clocks" or "a certain pair of nodes start along and lock edge change ". In fact, this constraint command does not have any ability to interfere with hard model content. Okay! The above is just a warm-up. Next we will slowly dissect the set multicycle path command.

Set multicycle path this constraint command will actually change when the startup or lock edge is triggered ., when we use the set multicycle path to tell timequest that a certain node uses N clocks to work, at best this is also the delusion of timequest, because the actual HDL behavior or hard model has not changed.

I need to emphasize that in the delusion of timequest, delay monster uses five clock periods, or the delay monster has five clock module cycles. However, delay monster uses only two clocks for its actual HDL behavior, or the actual delay monster has two clock module cycles. Of course we will not be able to accept this kind of improper horse head situation... here we should change the delay_monster's HDL content.

Set false path: timequest ignores related node analysis.

In fact, the compiler is not smart enough to automatically optimize the timing violations caused by the delayed monsters. Therefore, we need to constrain the relevant nodes. The command used includes the set multicycle path, which tells timequest to use N clocks for a node, in fact, it tells timequest to change the triggering behavior of the startup or lock edge of a node. Although the use of this constraint command can make timequest analysis enough to solve the problem, it leads to the difference between timequest and actual HDL behavior. Therefore, be careful when using it. In addition, set false path is an unreasonable constraint command, which requires timequest to ignore related nodes. Before using the set false path, it is best to confirm whether you have enough theory. If the delay monster in Experiment 5 exactly works with only two clocks, it will be self-defeating to use this command.

Derive_pll_clocks is a lazy create clock constraint command specially designed for PLL.

 

Summary:

(1) Remember That derive_pll_clocks is used to drive all the clock constraints of the PLL.

(2) learning to use the set multcycle path and understanding the set multcycle path cannot change the actual hardware model.

(3) set false path is used to make TQ ignore the corresponding node.

 

Motivation for learning timequest with black gold (3)