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24 Threads found on edaboard.com: Target Skew
If we meet setup and hold,but if we not meet skew as given target skew this any problem.
Hi, skew is in a way decided by the process technology you are using, and the methodology you want to use for timing closure. It may be also dependent on the design and the floor plan. For 0.13um to 0.18um, 250ps should be reasonable. A smaller skew will give a slightly larger latency. In general, the tool will build a tree with the smallest
Hi, I am working on a design using Magma Blast Fusion in which the clock period is 7ns. After CTS i am getting the following values in ps, Global skew 310. Local skew 293. Minimum Insertion Delay 525. Max
There is no problem. skew is a means to an end, not an end in itself. If all you setup and hold times are OK, then everything is fine. That said, many layout teams insist on achieving the specified skew target because they believe it makes the circuit more robust against variations.
For a foundry process, you will have been given the Spice model for the target (normal) process and models for Fast and slow nmos and pmos. You should run simulations for all variations e.g. nmos pmos N N F N N F S N N S F F F S S S etc, etc
How do we arrive at slew , derate values .I mean based on what slew limit are derates values are decided ?R they depends on technology nodes ? When clock gating helps in minimizing temperature then y we not consider clockgating helpful in minimizing leakage ? What r the factors that affect jitter ? why slew target should be met ? W
quality of CTS engine depends on how low skew & latency values it is providing while maintaining the level of clock tree structree and hw many buffers its inserting so generally it is followed to give a 0ps target for both in first iteration and from this iteration reports, set the target for both parameters for next iterations,, but for (...)
i will go with 0.5ns, As skew is matter only when am thinking if my design has just met target freq.
The highest clock frequency of design is 2M. Does 2ns trsnsition target tough for CTS? This is my first time to do CTS.
No DC will not do this. This needs to be done by the user. He has to estimate the target skew or uncertainty and give this to the tool. Normally we go with 10-15 percent clock period as uncertainty. But this depends on the design also.
hi, How Clock skew and latency of a design will change with respect to target clock period i mean, if i decrease/increase target clock period, how the skew/latency changes, if changes how/why they change? is skew/latency are depend on target clock period?
You need target skew, clock buffer list, max trans constraint for sinks , max trans constraint for buffers & max Cap too. You have some target for insertion delay, then give that too, otherwise in first pass let the tool build clock tree. Then for better optimization you need custom ignore pin list, leaf pin group & through pins .. (...)
#---------------------------------------------------------------------------- # Set option values set verbose 0 ;# 1 for verbose source commands set noscan 1 ;# False path the SCANEN input set signoff 0 ;# Use post layout netlist and parasitics set spef 1 ;# Use spef or dsp
hi , In my ASIC design, after finishing layout i checked for the timing, the static timing analysis gave a results as follows, setup slack => 3326 ps, hold slack => 10 ps, the target frequency of this design is 40MHZ(ie 25ns time period) my doubt is that the hold slack margin 10ps is it enough, else what range of values t
Hi osbourne, You seems to have 3 clock signals as input of your design and may be only two clock route available (buffer + global route)... Which device do you target ? Do you really need 3 input clock ?
1. Questions regarding the Synopsys Setup file synthesis. Why link lib and target lib is required and order of search path . 2. clock constraints like uncertainty, clock jitter, skew and etc. 3. explain about timing path. 4. how to specify IO delays. 5. Max dealy significance. 6. Optimization techniques. Best of luck.. Regards,
The skew target for your CTS is easy - it is simply the clock uncertainty that was assumed during synthesis. It is typically given in the SDC file. If you want to know what clock uncertainty value you should choose, well that depends on your process technology and your clock speed. Obviously, a 200ps skew is not easily achievable at 130nm, (...)
Hi, You would see these constraints before place and route, before we have a clock tree for the specified block. Adding more uncertainity to the setup part is over-constraining the block, This could be done by running the block at higher frequency i.e 10% more than u r target frequency(Just an example, percentage depends up on the designer). Ove
I select the ss corner library as the default target library. Obviously, it results in the lowest work frequency after dc synthesisi. I wonder this gate level result will unconditionally pass the ff corner timing constrains ? how to verify the robustness under all corner ?
I usually add a clock uncertainty margin to account for expected OCV at synthesis / pre-cts (on top of expecteted skew and jitter margins.) OCV increases with delay of the non-common clock path, so consider that and your ASIC vendor's suggestions for the target process when increasing the clock uncertainty for OCV for different clocks.
Can you elaborate more on how CTS screws up? The latency value specified is picked by CTS as the skew target.
Hi, It depends on lot of things... - Fanout of your clock which you cannot control - The cells your are using to build the tree. Try using higher drive cells. - Max tran limit you have set. If it is very tight it will increase your levels. - skew target - Also check your clock grouping to make sure your are not balancing the clocks which need no
By default, EDI picks the clock uncertainty value as the skew target in the clock spec file.
My question after clock tree expansion why do we target setup first and then hold and why not vice versa.