Sage-Tips

What are skew groups?

Skew group is nothing but a group of clock sinks. The clocks which have similar source (and which are synchronous to each other) are placed in a group. However, two different groups are logically exclusive. Hence, the tool will try to improve skew and balance latencies of the groups independently.

What is skew physical design?

Clock skew (sometimes called timing skew) is a phenomenon in synchronous digital circuit systems (such as computer systems) in which the same sourced clock signal arrives at different components at different times. The instantaneous difference between the readings of any two clocks is called their skew.

Why is skew important in VLSI?

The reasons are: The insertion delay to the launching flip flop’s clock pin is different than the insertion delay of capturing clock (like maybe capture clock is coming before then the launch clock or capture clock is coming after the launch clock that difference is called skew) The clock period is not constant.

What is skew in layout?

Clock skew is a phenomenon where clocking signals arrived at different destinations at varying intervals. Clocking signals are commonly used for synchronous communication in PCB design. The difference between the arrival time of the clock signal and the receiving pins is the skew value.

What is useful skew?

If clock skew is used intentionally to meet timing then it is called useful skew. P&R tools can use useful skew as an optimization option in CTS and other stage optimizations to leverage the clock signal in meeting timing, with acceptable margins.

What do you mean by useful skew and how it impacts the timing?

Useful skew-If clock is skewed intentionally to resolve violations, it is called useful skew. Since Setup slack = required time (clock) – arrival time (data) if i reduce the required time my slack violation will cease.

What is skew grouping in VLSI?

Creating Skew Groups: Skew groups are basically groups of sink-pins (clock end-points) which need to be balanced against each other. Now, some skew groups may be default, some might need to be created explicitly to help CTS engine.

What is skew group in VLSI?

What is skew signal?

Skew is the time delta between the actual and expected arrival time of a clock signal. Skew can be either extrinsic or intrinsic. The latter is internal to the driver (generator circuitry) and defined as the difference in propagation delays between the device outputs.

What is skew in signals?

What is the importance of useful skew?

Our tool generates ‘useful skew’ with safety margins to guard against timing violations.” Xi said “useful skew” adjusts the effective timing constraints on data paths, so designers can reduce the number of design iterations and achieve timing closure by focusing on just one signal — the clock.

What is the difference between a skew group and skew group?

– Clock sinks that are not defined in any skew groups are automatically included in the default skew group. – A skew group is independent when only clock sink pins are defined in the group.

What is useful skewing?

After borrowing the skew, we can see that in below picture the skew looks positive in number for all the three paths. This concept is called as useful skewing and the skew we borrowed is useful skew.

What is skew group in ICC?

You can selct a group of clock sinks from the same clock domain to form a subgroup named a skew group. ICC automatically balances the skew of clock sinks, including the clock pins of integrated clock-gating cells, enable flip-flops, and clock dividers, in each skew group.

What is useful skew in P&R?

If clock skew is used intentionally to meet timing then it is called useful skew. P&R tools can use useful skew as an optimization option in CTS and other stage optimizations to leverage the clock signal in meeting timing, with acceptable margins. Let us first see an example of clock being skewed to meet timing.