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- <title>Oscillation errors</title>
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- <h1>Oscillation errors</h1>
- <p>The propagation algorithm, which normally works silently without any
- problems, will become very visible
- when you create a circuit that oscillates.</p>
- <center><img src="../../../../en/img-guide/prop-oscillate-before.png" width="335" height="223"></center>
- <p>This circuit is currently in a stable condition. But if you change the
- input to 1, the circuit will effectively enter an infinite loop. After
- a while, Logisim will simply give up and show an "Oscillation apparent" message
- telling you that it believes that the circuit is oscillating.</p>
- <center><img src="../../../../en/img-guide/prop-oscillate-error.png" width="335" height="223"></center>
- <p>It will display the values it has at the time it gives up. These values
- will look wrong - in this screen shot, the AND gate is emitting 1
- although one of its inputs is 0, but it could be that the NOT gate
- has a 1 input and a 1 output.</p>
- <p>Logisim helpfully circles in red each location that seems to be
- involved in the oscillation. If an involved point lies within a
- subcircuit, Logisim will draw that subcircuit's outline in red.</p>
- <p>When Logisim detects oscillation, it shuts down all
- further simulation. You can re-enable simulation using the
- Simulate menu's Simulation Enabled option.</p>
- <p>Logisim detects oscillation using a fairly simple technique: If the
- circuit simulation seems to many iterations, then it will simply give up
- and report oscillation. (The points it identifies as being involved are
- those that were touched in the last 25% of the iterations.)
- Thus, it could erroneously report oscillation,
- particularly if you are working with an exceptionally large circuit; but
- it would be one that is larger than any I have built using Logisim.
- In any case, if you are confident that the reporting is in error, you
- can configure the number of iterations
- completed before oscillation occurs via the
- <a href="../opts/index.html">Project Options</a> window's
- <a href="../opts/simulate.html">Simulation tab</a>.</p>
- <p><strong>Next:</strong> <a href="shortcome.html">Shortcomings</a>.</p>
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