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Hi, What exactly is the concept of useful skew in flop based designs and time borrowing concept in latch based designs. Vicky
As the skew increases(positive skew)the setup requirements are reduced. ie.. a circuit synthesised for 150 Mhz may run at 170 Mhz, considering the Clock skew associated with the registers. inshort useful skew refers to the skew which relaxes the timing constraints on the design.
What is the "useful skew" in SoC Encounter and how to use it? Is it part of an ECO process? Thanks
Can anybody explain useful skew?How its useful in design with respect to setup and hold?
refer this pdf it give u some input about usefull skew
hi all, what the major difference between zero skew and useful skew ? in what case we will use useful skew and zero skew and what about timing issues needed to considered and how we can increase clock frequncy with this useful skew i will (...)
It'said that the design using useful skew for timing optimization is susceptive of the operating condition variation-temperature,voltage,process... And why? zero skew clock tree also have clock buffers which have PVT variance.
What is useful skew and how is it used?
omg so many questions in one post:D........kidding useful skew: when u insert delay in clk path to meet setup slack ... adv: very critical setup can be met disadv: hold might worsen( so should take care of hold) only when one cant meet timing then only one go for useful playing with clk path not recommended.... anyone can co
Hi As far as I know, there will be no pre CTS useful skew.. AS the clock is considered as ideal in pre CTS stage. Post CTS useful skew helps in meeting the timing for critical paths.. If you have a critical path violating timing by 1ns in a 10ns clock and the next flop is meeting the timing by 8ns itself (when (...)
Hi All, I need documents related to useful skew..........
Hi all, what is useful skew? what will do in Encounter...... Thanks
we can opt timing use useful skew after CTS,and at that time,the clock tree fixed,and the useful skew is based on the fixed clock tree I right? If I'm right,I am wanding when doing CTS,can I tell the SOC-encounter that I will use the skew latter,then the software will not fix some skew that (...)
What is the difference between skew and useful skew?
what is useful skew.how will come useful skew?
We usually build a zero skew clock tree first when clock insertion. But If there are some timing violations, we will try to build a useful skew clock tree. The useful skew is the manual skew we add on the clock tree to balance the current timing path and the next timing path.
What is useful skew with respect to CTS?.
Hi ajesh, The discussion in the following thread will answer your query.. if you still have any doubts please post here... useful?? cheers
You cannot always fix all violations using useful skew. useful skew can be used only when you have enough slack on next/previous stages. Without slack values and how much clock tree exception was set, its hard to figure out the issue, but my guess is that you probably went overboard with 'useful (...)
Ans to What is Clock skew ? -- In circuit design, clock skew is a phenomenon in synchronous circuits in which the clock signal (sent from the clock circuit) arrives at different components at different times. This is typically due to two causes. The first is a material flaw, which causes a signal to travel faster or slower than expected. The seco
Some of the things you can do are . . . - Rebuffering the clock trees - Balance Clock Trees (either rebuffering or by routing) - Try playing with useful skew -- ay
Another disadvantage - Cannot take advantage of 'useful skew'. useful skew - Clock skew between adjacent filpflops effectively increases the clock period for the same clock frequency, so path delay negative slack is reduced. (slack = effecrive clock period - path delay - setup time).
hi Energeticdin, my 2 cents to your queries. Whether Positive skew is good for Setup? How? positive skew is similar to useful skew , it is nothing but delaying capture clock by skew value correct than the normal launch clock value when ever you delay the capture clock surely you gain that my margin (...)
What is useful skew?
First a correction: sd and ss are not skews, they are the insertion delays to those registers. Their difference is the skew. Yes, skew can be beneficial in some cases. It is called "useful skew". The idea is that one register-to-register stage can have plenty of positive slack while the next stage has a (...)
Significance of Global skew is one need not perform CTO as Setup and Hold Check is already done as useful skew optmizises in such a way that there is no setup violations. For more info:
Hi Kumar, In all probability there will be setup and hold violations along various paths..depending on whether there are positive or negative skews at the end points... But the thing is we may use the same skew for fixing these violations..this is referred to as useful skew...intentional placing skew to (...)
Hi Kumar, Yes skew effects hold time calculation.. positive skew will lead to hold violation while helpful for setup fixes negative skew will lead to setup violation while helpful for hold fixes we will use skew balancing and useful skew concepts in this kind of scenarios... cheers,
jaya sree, latency numbers can be accepted. Can you tell me if clock skew numbers are global skew or local skew? By any chance did you turned on use of useful skew to meet timing? if that is the case and your timing is good. no need to worry. Jay
For me, usefull skew is the skew between flops which have timing path in common. I means, the (normal) skew, is for all flops independently if these flops have no common paths.
hi, using magma tools or cadence clockwise to generate clock tree. they can use useful skew to improve the performance.
Pinkesh, search the forum friend.
why some skew is usefule?please give me an example,tks!
shankarmit gives a description from on side. And I think it maybe another CTS types: global skew synthesis, local skew synthesis and useful skew synthesis. Global skew : consider the skew between all registers Local skew: only consider the skew (...)
Hi, It has become necessary to perform hold analysis in worst case corner. I can think of 3 reasons: 1. useful skew. If there is a large skew in the clock tree (e.g. to meet setup time), it is possible that this can cause a hold violation in worst corner, but not best corner 2. Negative setup and negative hold in worst case cell (...)
Hi, Clock latency to every flip-flop is different. The different in the clock latency between two flip-flop is the clock skew. The clock skew can affect the timing budget between the flip-flops. useful skew is the technique to skew the clock so that you have more timing budget on the critical paths.
add some skew to clock that is useful skew to improve frequency. Restructure the logic . use latch based design. put the combinational part which takes more time in data path in next or previous logic. add slow signals near to output ,so critical path delay can be decreased . Flattten the deisgn ,instead of structuring or factoring. bye
PT, as far as i know, can't fix the timing violations. but, hold violations are fixed using buffers in the P&R stage, or by adding an additional flop(making sure functionality is met) in the RTL stage. For setup violation, either better constraints or methods such as inserting buffers in the nets or useful skew are used in the backend stage.
For setup violations you need to reduce the datapath delay, which is what datapath optimization does, or decrease the clock speed. For hold violations , you generally need to delay the clock, which can be done by adding delay in the clock path, or by using useful skew.
Hi all, Please clarify me, What is capacitive loading? How does it affect slew rate? What is useful-skew mean? Din
Hi all, 1. How operating voltage can be used to satisfy timing? 2. What is the difference between local-skew, global-skew and useful-skew? 3. What is meant by virtual clock definition and why do i need it? 4. Is it possible to reduce clock skew to zero 5. what are problems associated with (...)
1. FloorPlan Utilization Slack with zero interconnect delay 2. Placement Timing numbers,utilization,repeater count,VT percentage,cong,cell density,useful skew,clock gate placement(if any),cell hierarchy,cells in the macro channels 3. Ideal Clock IPO Same as placement 4. CTS clock latency,global skew, local skew,CT (...)
i've that book... i want to know about useful skew,local skew ,global skew and all those things..it's not given in this book Dear Biku, useful skew:- This is the min skew required to meet both setup and hold violations of a path. Sometimes, what happens, when we (...)
Every Flip-flop has setup/hold window around active clock edge. Setup before edge, hold after. In shift registers data pass from Q-out of previous flop to D-in of the next flop directly, so it have minimal possible delay. Data can pass to D-in inside hold window. To fix this violation you should put delay buffer from Q-out to D-in. Another factor
Hi tachyons, Please refer & for setup and hold fixing Hope you find it useful... PS: lot of questions in one day..hmm
Hi gokulka, Firstly, clock skew and clock latency (related to clock tree depth) are the most important problems to solve in clock tree synthesis. Secondly, design rule violations such as maximum transition on clock pins, maximum capacitance, maximum fanout, and clock bumps (signal integrity issues) are important factors. For a typical desi
also check local and useful skew concepts, know how and where you are going to apply these to time your paths better.
There are many other methods than sizing to fix setup violations. 1. Logic restructuring: Reduce combinational logic delay by minimising number of logic levels. 2. Vt swapping: Sweeping HVT by RVT or LVT. Standard cell library has three type of cells. HVT(High threshold voltage), RVT (Regular threshold voltage), LVT (Low threshold
You can give CTS a try since useful skew and placement can improve your timing. But I don't suggest it. 170ps should be fine enough to proceed.
many ways to fix setup violation after synthesis. 1. size cell and minimize data path delay. 2. check hold margin and useful skew. 3. use LVT cell if all ways can not work. you 'd better add more margin to re-synthesis or re-design.