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What is a combinational feedback loop?
A combinational loop is created when the output of a logic gate is fed back into the same exact gate, or another gate earlier in the combinational path, but no sequential is involved.
What are combinational loops?
Combinational loops are loops in combinational logic, with no registers between any of the nodes. The Timing Analyzer analyzes combinational loops very conservatively in order to ensure that only legitimate timing violations are detected in the design. Large combinational loops are usually the result of a design error.
Why to avoid combinational loop?
A design should not contain a combinational loop, which is combinational logic that drives itself without being synchronized by a register. The following image shows an example of a combinational loop: These combinational loops can cause significant stability and reliability problems in a design.
What is a timing loop?
Combinatorial timing loops are created when the output of combinatorial logic is fed back to its input, resulting in a timing loop. This loop unnecessarily increases the number of cycles by infinitely going around the same path and cannot be timed.
What does a for loop do in synthesizable code?
For loops in synthesizable code are used for expanding replicated logic. They are simply a way of shrinking the amount of code that is written by the hardware designer. They do not loop like a C program loops. They only expand replicated logic.
When does feedback stop in combinational oscillations?
Imagine b = XOR of a and b. a changes to 1 output changes to 1 loops back xor is now 0, feedback means xor is now 1 etc. This is an uncontrolled oscillation which will only stop when the input a is set 0 and it will stop in an undetermined state.
How to detect a combinational feedback loop using VCS?
Then run the simv using +vcs+loopreport. You may see loop report. command. This directly gives you the loop info. Synopsys VCS can also help you in this requirement. time switch. Then run the simv using +vcs+loopreport. You may see loop
Which is the best description of a feedback loop?
Common terms that could describe positive feedback loops or cycles include “snowballing” and “chain reaction”. Without a counter-balancing or “shut-down” reaction or process, a positive feedback mechanism has the potential to produce a runaway process.
How to detect a combinational feedback loop in Irun?
This directly gives you the loop info. Synopsys VCS can also help you in this requirement. time switch. Then run the simv using +vcs+loopreport. You may see loop report. command. This directly gives you the loop info. Could you please tell me similar one in irun (Cadence incisiv simulator)?