Automatic Mirroring and Pin Permutation During Abutment

If an attempt to abut two devices causes two pins on the same net to touch, a short violation is created. Layout XL tries to resolve this violation automatically by first mirroring the device or chain in question. If that fails, it then attempts to resolve it by permuting pins.

This behavior is controlled by two environment variables, both of which are switched on by default.

• autoMirror which specifies that if a short violation is created during abutment, then Layout XL first mirrors the device in question in order to resolve the short. Only if this is unsuccessful does Layout XL attempt to resolve the short by permuting the pins.
  The GUI equivalent is the Mirror transistors option on the Layout XL Generation Options form.
  Automatic mirroring is temporarily disabled when constraint-aware editing is on and constraints exist between the instances and chains under consideration.
• autoMirrorChains which specifies that device chains are mirrored subject to certain conditions being satisfied. This environment variable is honored only if auto Mirror is set to t. It has no GUI equivalent.
  If one of the devices is in any type of group (including a synchronous clone), the other device must be in the same group for automatic mirroring to occur. Mirroring is done on end-pin violations only if they are valid left/right or top/bottom pairs.

To disable the mirroring of devices and chains:

1. From the layout window menu bar, choose Options – Connectivity and click the Generation tab.
2. Switch off the Mirror transistors option and click OK.
   This switches off both device mirroring and chain mirroring during abutment.

Resolving shorts by mirroring rather than permuting pins is desirable because pin permutation

• Assumes that the device is symmetric and therefore the source and drain parameters are not swapped
• Changes the connectivity of the design.

Resolving the short violation through mirroring removes these drawbacks. No pin permutation is performed on chained devices.

Related Topics

autoMirror

autoMirrorChains

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