Chapter 9: Tools
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9-6: Routing
9-6-2: Auto Stitching |
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The auto-stitching router looks for adjoining nodes that make implicit connections,
and places wires at those connections to make them explicit.
For example, if a cell has power and ground rails at the top and bottom,
and there are ports on the left and right of each rail,
then the auto-stitching router can be used to connect all of these rails in a horizontal string of these cell instances.
The auto-stitcher places a wire when all of these conditions are met:
- The design is layout (auto stitching does not work in schematics).
- Ports exist on both nodes.
Because wires must run between two ports, you must make exports at every location where wiring may occur.
If "Create exports where necessary" is checked in the Routing Preferences
(in menu File / Preferences..., "Tools" section, "Routing" tab),
then it is not necessary to have ports at all connection sites: the router will create them for you.
- The nodes inside of the cells
(the ones with the exports)
must touch or overlap, thus creating an implicit connection.
When a pin node has an export, it should be the same size as any wires connected to it inside of the cell.
This is because a small pin which is deep inside of a wide arc will not make an implicit connection when the arc touches something.
- The ports must not already be connected to each other.
To run the auto-stitcher, use the Enable Auto-Stitching command (in menu Tools / Routing).
The router will make all necessary connections, and incrementally add wires as further changes are made to the circuit.
To stop stitching, select the menu entry again to disable it.
To run the auto-stitcher only once for the current cell, use Auto-Stitch Now
To run it once, and in the highlighted area only,
use the Auto-Stitch Highlighted Now command.
Note that this auto-stitches all cell instances that intersect the highlighted area,
so even if only a portion of a cell falls into the highlighted area,
the entire cell is stitched.
The auto-stitcher allows you to specify a particular type of wire to use in routing.
By default, the router figures out which wire to use.
However, in the Routing Preferences a specified wire can be given
(or automatic selection can be resumed by selecting the "DEFAULT ARC" entry).
First check "Use this arc in stitching routers" and then select the arc.
