# Questions tagged [timing-analysis]

Timing analysis is the process of determining whether a circuit will meet its timing requirements, given the characteristics of the components in it.

112 questions
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### Why double synchronizer alone is not enough for multi byte transfer between two clock domains?

When one bit information is transferred between two different clock domains, we use 2 Flip-flops or double synchronizers. But when we transfer multi bit signals across two different clock domains, why ...
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### How to measure FPGA execution time of combinationals blocks [on hold]

I have written a combinational block which makes some math operations. What's the best way to calculate the time elapsed in that block? Thanks in advance!
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### Setup and Hold Time: A general method to find whether a block satisfies the constraints

How to determine whether setup and hold time constrains are satisfied in a digital block? I encountered a question on the same, and it would be really helpful to know a general way to determine the ...
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### Timing Constraints for Forwarded Generated Center-Sampled Clocks?

Problem Description I am trying to figure out the "correct" way to constrain (in .xdc format - this is in Vivado) a forwarded source-synchronous clock that is generated (by division) from the ...
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### In Intel Quartus Static Timing Analyzer should -ve setup slack on a path in Slow_900mV_0C model also show up in Slow_900mV_100C model?

I am trying to understand why the paths with -ve slack in Slow_900mV_0C model do not show up in Slow_900mV_100C model. I am using Arria 10 GX. I would think the process part of the model is likely ...
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### SR latch timing diagram or waveform with delay, help!

I'm having trouble solving these two problems (my solution and general solution showed): What I did was follow the truth table and based on the combination on the graph draw the appropriate state ...
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### Why only shared resistances are taken into consideration while computing Elmore delay?

While we compute the delay , using Elmore delay model we take into consideration the shared resistance and capacitance. I would like to know why are we only concerned with shared resistance not the ...
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### Best practice for synchronizing VHDL stimuli with circuit

What is the best practice or method for synchronizing stimuli input and output with a sequential logic block in VHDL? I am currently running only behavioral simulations, but I want to make sure my ...
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### Why Static Time Analyzer (STA) Engine doesn't show fmax for Fast Model?

I'm working on Intel FPGA. The Timing Analyzer (STA Engine) gives Fmax summary for both slow Models but none for the fast model WHY?. I didn't find any setting for this in documentation or in GUI. (...
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### Generating a specific sequence of signals in Verilog with timing requirements

I am a beginner in Verilog, and as a part of a project, I have to send a sequence of signals to a chip in order to program one of its parameters. This Verilog code will be synthesized on an FPGA, and ...
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### Synopsys Technology File (STF)

I am using a memory IP block from STM. The manuals of the memory IP has talked a lot about Synopsys Technology File (STF), though, with no info on how and where to use it. Among all files related to ...
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### Timing issues in netlist simualtion - SDF simulation of IP block

TOOLs and Tech: Questasim 10.5c-2 / Synopsys design_vision I-2013.12 / STM 65nm Hi I am running some timing simulations on my design and have some doubts and issues with the results. 1- My design is ...
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### Relationship between clock skew (For Reg-Reg path) and minimum clock pulse width requirement for capture Flop

I am hoping if some expert in timing analysis could answer on this topic. Here is the question: I am creating a liberty timing file for an IP block using ETM (Extracted Timing Model) method. ...
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### Non-optimal clock IOB/BUFGMUX placement correctable in software or hardware?

I am getting this nasty error when synthesizing my design using ISE Studio for Spartan-6: ...
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### Multiple Reset Synchronization

I have two active low async resets (rst_na and rst_nb) and associated two clocks (clk_a and clk_b). Assume Block B required ...
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### Data path in logic circuit

In the fig below is the path from CLK of 1st FF to Output(DataOut1) a valid data path. If so why is it not shown? Is it because its just the combination of PATH2 and PATH3? Thanks.
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### How to properly constrain generated clock and synchronizer in Altera Quartus?

In my Verilog design I have a 25Mhz board clock from which I derive a 100Mhz clock. Coming from an external Pin I have an asynchronous 4.77 Mhz clock which should drive the logic and be synchronized ...
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### Timing the change mode (Read/Write) on SD card

I'm currently working on a device which connects a SD card to a FPGA. I have to find out how much time the SD card takes to switch between the reading and writing modes. I have already searched the ...
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### How to estimate timing contraints for FPGAs?

I try to find out how to specify the timings restrictions in FPGA designs correctly (in .sdc/.xdc files). I know what setup and hold times mean. However: How do I find out, what timing constraints my ...
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### doubt regarding max/min value of clock skew component in setup time equation

Kindly help me to out with the following questions asked in a recent interview: Theoretical Max and min value of clk skew in the equation of the setup time? Practical Max and min value of clk skew ...
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### Why the simulation time of a synthesized netlist depends on the clock period at which it is constrained?

I have a design which after synthesis at clock 500 picoseconds in dc_shell takes about 2 minutes to run the synthesized netlist against the testbench. The synthesized netlist worked as expected. ...
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### How do you determine if a chip has either hold or setup violation after it has been manufactured?

Suppose a chip was taped out without proper timing analysis. After you get the chip back, what kind of testing is done to check if there are any setup or hold violations in the chip?
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### Negative slack while designing a feedback controller using Xilinx System Generator

I'm transforming the design of a feedback controller(PI controller) which was already in Simulink, to FPGA using Xilinx System Generator. The main design problem i'm facing is the negative slack time....
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### SPI interface on Xilinx FPGA, clock domains and timing constraints

I am interfacing a Raspberry Pi board to a dev board with a Spartan 6. I want to do this using SPI. Because of the way the dev board is designed, I need to connect SPI CLK and DATA to standard IO pins....
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### EEPROM 25LC1024 issue with PIC32MX OLIMEX board

I am trying to read the status register for the EEPROM following the instructions in this Application Note. I wanted to have the opinion of the community on the signals I am getting. They don't seem ...
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### Should we use asynchronous inputs in Moore blocks and synchronous in Mealy blocks?

Consider we have two n-bit counters CNT_A and CNT_B two n-bit unsigned comparators CMP_A, CMP_B and two n-bit binary numbers N1, N2. The counters have two inputs C, L for synchronous count and load ...
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### How to constrain a clock signal out from a multiplexer

How would you constrain this design? ext_clk and clk_in are asynchronous to each other. clk_div is derived by clk_in with double period. clk_out may be driven by either clk_in and ext_clk, ...
884 views

### Minimum Clock Period from setup and hold time

I found several different answers to how setup and hold-time of Flip-Flops influence the minimum time between two rising clock edges. tclock >= Propagation delay + tsetup + thold tclock >= ...
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### Intel/Altera FPGA bidirectional DQS timing constraint

I have a DDR controller implemented in an FPGA using Altera/Intel/Quartus, and I'm trying to get the constraints correct for the bidirectional DQS pin. This pin is a data strobe pin that the DDR ...
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### Is it possible to estimate the execution time of an FPGA design?

Is it possible to evaluate the "execution" time of an FPGA design? I think that if you have a design where you only have And, Or, Not, etc. gates, the result only depends on the inputs. But now with ...
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### Temperature and Voltage variation affects on Metastability

Are there any effects of temperature and voltage variations on Metastability of the flip-flop? If Yes, What are the effects?
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### Is post fit simulation using timing netlists necessary although design meets setup-hold time requirements?

In a purely synchronous design, if the design has positive slack for setup and hold times, it means that it meets timing. Therefore, provided that we have carried out static timing analysis and are ...
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### Generation of non overlapping clocks on FPGA using VHDL

I am trying to implement switched capacitor circuits and I hence need to generate a two-phase non-overlapping clock. I have been trying to use an FPGA for the same. Unfortunately, my synthesis tool- ...
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### How do I give clock constraint for a ring oscillator output?

I have 2 clocks in my design. One slow External clock and one high frequency ring oscillator clock. For external clock I am using the create_clock command to specify timing. The ring oscillator block ...
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### Thoughts on this circuit

Here I have a design ( Vcc = 12V ) where relay gets activated whenever reed switch gets closed. I want to activate the relay after a delay of about 2 to 3 seconds from the instant reed switch gets ...
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### Using both clock edges in an FPGA design

So, after getting some advice from some good people here, I managed to put together my first (very modest) FPGA design. It is basically just a few registers and counters, and only runs at a few MHz, ...
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### Timing closure suggestions

I've a FPGA design ( I didn't write a single line of sources code) and I've to add a module ( in the design there is a Wishbone bus where it's possible to link others wishbone interface ). The modules ...
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### SDC constraints for two flop sychronizer

I have doubt, What should be proper SDC constraint for CDC module, i.e., two flop synchronizer. between "dat driving by aclk to <...
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### Edge aligned Source synchronous outputs

This is a basic block diagram of source synchronous interface I found in altera document. Here This is how edge aligned source synchronous output looks like. They say the reciever will shift the ...
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### Use of clock in SDC style IO constraints for FPGAs

Question on use of clock in SDC style IO delay constraints The intention of this write up is to cast some clarity on how an FPGA IO interface has to be constrained. As a preamble the two timing ...
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### Vivado timing constraints wizard

I have an FPGA design that uses 2 outside clocks (INCLK and TXCLK) from an ADC to latch data also coming from an ADC (TXOUT) and a system clock. A defined INCLK TXCLK and clk_sys as primary clocks in ...
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### What are minimum requirements to start of with STA [closed]

What are the minimum requirements to start with static timing analysis. I know usage of FPGAs and VHDL. Will that be enough? Are there any free tools for STA pls.?
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### Is it possible to find the critical path in specific part of the design?

I have written RTL description of a circuit in VHDL which is hierarchical and I am using Altera Quartus II; my design meets timing. I had set 50MHz clock frequency (20ns period) constraint using ...
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### How to calculate latency of a circuit?

Lets say we have this circuit: tpd(AND)=5 ns, tpd(OR)=5ns, tpd(NOT)=3ns, and tcd of all gates =1ns FlipFlops: tpcq=1ns, tccq=1ns, tsetup=1ns thold=1ns First I want to check this circuit for hold-...
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### FPGA: intentional delays through manual placement/routing

In my FPGA design, I have some input signals that need to be delayed considerably before they reach the first clocked register. There are delay elements near the pins for exactly that purpose, but ...
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### how to get the timing report register to register and input to output in STA?

I'm trying to get the timing report of STA. As I know, basically, there are 4 types of timing paths. Input to register Register to register Register to output Input to output Practically, I want to ...
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### FPGA Internal Timing constraint failing

I'm currently trying to implement an IP-Core on a Cyclone V 5CSEBA6U23I7 FPGA-HPS System using Altera Quartus II and TimeQuest Analyzer. The Verilog code pasted below produces a timing problem, namely ...
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### Synchronize Outputs of Separate FPGAs Within 1ns

Edit: I have been able to achieve 560ps uncertainty in simulation by using external PLL feedback through the entire chip. Once I verify in real hardware I will post a complete solution. I'm trying to ...