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<!-- COMMAND Tools/Routing/Sea-Of-Gates Cell Properties... -->
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The sea-of-gates router is able to take an arbitrary set of unrouted arcs and convert them to layout.
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It also honors the "Routing Exclusion" nodes to restrict certain metal layers
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(see <A HREF="chap09-06-01.html#chap09-06-01">Section 9-6-1</A>).
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To do this, use the <B>Sea-Of-Gates Route this Cell</B> command (in menu <B>Tools / Routing</B>).
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To run it, use the <B>Sea-Of-Gates Route this Cell</B> command (in menu <B>Tools / Routing</B>).
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If there are unrouted arcs selected, these will be the only ones converted.
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Otherwise, all unrouted arcs in the cell will be converted.
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If sub-cells below the current cell need to be routed, use <b>Sea-of-Gates Route Sub-Cells</b>.
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The router has many features that can be controlled by the Routing Preferences
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and by cell-specific properties.
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<h3>Sea-of-Gates Routing Preferences</h3>
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The router can be controlled by the Routing Preferences and by cell-specific properties.
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The Routing Preferences (in menu <B>File / Preferences...</B>, "Tools" section, "Routing" tab)
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<li><b>Search complexity limit</b> sets the maximum number of steps that
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the router will take to find a route.
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The larger the value, the longer the router will run before it gives up.</li>
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<li><b>Maximum search factor</b> controls the maximum area that will be considered for a route.
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This value is multiplied by the largest design-rule spacing, so a factor of 10 and a maximum
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spacing of 15 means that the router will consider up to 150 units outside the bounding rectangle
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<li><b>Do Global Routing</b> requests that a global routing preprocessing step be done
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to plan the path of each route.
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Global routing divides the cell into a grid, and forces each routes to run in certain grid squares.
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<li><b>Rerun routing with failed routes</b> requests that the router run again
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after it finishes in an attempt to complete those routes that failed the first time.
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You can set a different complexity limit for this step.</li>
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<li><b>Run even on connected routes</b> requests that the router connect points
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that are already connected geometrically. When unchecked, routes that already connect
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are ignored by the router.</li>
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<li><b>Contact options</b> There are four ways to place contacts in the routed circuit:<ol>
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<li><b>Contacts at top level</b> place contacts where they are needed at the top level of the cell.</li>
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<li><b>Contacts use existing subcells or place at top</b> look for subcells that have the desired contact geometry
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and place instances of those subcells instead of actual contacts. Other contacts are placed at the top level.</li>
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<li><b>Contacts use existing subcells or create new ones</b> look for subcells that have the desired contact geometry
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and place instances of those subcells instead of actual contacts. Other contacts cause new subcells to be created.</li>
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<li><b>Contacts create new subcells</b> all contacts are placed in newly-created subcells.</li>
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<li><b>Use two processors per route</b> tells the router to use two threads for each route
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(one tries to run a path from end 1 to end 2, the other tries to run a path from end 2 to end 1).
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The thread that completes first terminates the other thread.
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When not checked, the router alternates steps in the two directions, stopping when one of
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the directions reaches its goal.
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Because the router is able to follow both directions in a single thread,
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this preference is not advised (it is better to use multiple processors for the next option,
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which runs multiple routes in parallel).
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However, on many-core systems, where there is excess computation power, this preference may be desirable.</li>
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<li><b>Do multiple routes in parallel</b> attempts to use as many processors as possible
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to run multiple routes at once.</li>
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the directions reaches its goal.</li>
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<li><b>Do multiple routes in parallel</b> uses multiple processors to run routes in parallel.</li>
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<li><b>Forced processor count</b> tells the router to ignore the actual number of processors
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on the machine and to use an appropriate number of threads for the processor count specified here.
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Set the value back to zero to remove the override.</li>
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on the machine and to use the specified number of threads.</li>
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You can then choose whether odd-numbered arcs are horizontal or vertical.</li>
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<li><b>Contact inclusion pattern</b> and <b>Contact exclusion pattern</b> let you specify which contacts in
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the technology to use for routing.
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You can also select contacts to use in 2X routing.
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For example, to force only contacts that start with the letters "X-", set the inclusion pattern to "X-(\w+)"</li>
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<li><b>Do not place rotated contacts</b> Requests that asymmetric contacts not be tried in a rotated orientation.</li>
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<li><b>Do not make Steiner Trees (already done)</b> Before routing begins, the unrouted arcs
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(multiple arcs on a single network that connect more than two ports) run in the most efficient way.
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This efficient path is called a "Steiner Tree".
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If you believe that the routes are already optimized, you can request that this step be skipped.</li>
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<li><b>Contacts down avoided layers</b> and <b>Contacts up avoided layers</b> Requests that nets which
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start or end on forbidden layers be allowed to place a contact up or down to a permitted layer.
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The contact cannot create new geometry on the forbidden layer, so the necessary area on that layer must
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<li><b>Routing bounds layer</b> sets the layer which will limit the bounds of routing.
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If geometry exists in that layer, the extent of the geometry will define the bounds of routing.</li>
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</TD><TD></TD></TR></TABLE>
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The lower-left part of the dialog controls individual layers in the cell.
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It lets you disable the use of any layer, or favor it above others.
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You can also override the default width and spacing rules on that layer.
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You can also request that a layer be a taper by setting a Maximum taper length
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Tapers are the initial or final segments
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of a route which use the width of the geometry at the end, rather than the default width.
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They have a limited run length.
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You can also request that a given layer be available only for tapers, and not for intermediate routing.
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For each layer, you can also override the default width and spacing rules on that layer.
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The "2X width threshold" is the width above which a wire is considered to be "2X" in size.
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When that happens, special contacts may be used, and mask colors are flipped
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(only relevant in technologies that have multiple masks on a layer).
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The <b>Remove Geometry Layer</b> is a layer which will remove the presence of the given layer.
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For example, if the Remove Geometry Layer for Metal-1 is set to a layer called "DM1",
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then the presence of the DM1 layer will actually remove any Metal-1 under it for the purposes of routing.
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And you can set a grid for placement of the layer.
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Grid control can be <b>Fixed</b> (with a spacing and an offset)
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Another layer control is the use of grids.
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Grids can be <b>Fixed</b> (with a spacing and an offset)
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or <b>Arbitrary</b> (with multiple grid coordinates).
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When editing arbitrary grids, icons on the right let you create new grid coordinates, delete existing ones,
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and even draw the location on the screen.
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Click <b>Show</b> to draw the grids on the cell to help you see where the grids actually are.
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The right side of the dialog controls individual nets that are to be routed.
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If nothing is listed on the right, then all selected nets are routed (or all nets, if nothing is selected).
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Use the "Add Net" button to add a named net and use the "Remove Net" button to remove a listed net.
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The upper-right side of the dialog controls individual nets that are to be routed.
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If nothing is listed at the top, then all highlighted nets are routed (or all nets, if nothing is highlighted).
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Use the <b>Add Net</b button to add a named net
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and the <b>Remove Net</b> button to remove selected nets from the list.
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When a net is selected, you can even override the layers that will be used to route that net
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and you can override the width and spacing rules for that layer on that net.
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The lower-right part of the dialog lets you add arbitrary rectangles in the chip on given metal layers
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which will act as blockages, preventing routing in that area.
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The "add" icon creates new blockages, the "delete" icon removes them, the "edit" icon modifies the selected blockage,
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and the <b>Show</b> button shows all blockages in the circuit.
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At the bottom, the "Import..." button reads a command file that can fill this dialog with values.
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