Chapter 9: Tools
9-6: Routing
9-6-7: Clock Routing

The clock router connects multiple clocked cells to a single clock generator, ensuring a constant wire length to each clocked cell. It does this by building tree structures in user-specified routing channels, adding serpentine wires if necessary to balance the length. The router can also insert balanced repeaters and can route multiple, independent trees, all with the same wire lengths.

The Clock Router is run with the Clock Routing... command (in menu Tools / Routing). The command prompts for a command file that specifies the clock routing task. The command file contains directives that describe the source and destination nodes, the routing channels, and other routing parameters. These are the directives that can appear in the command file:

Here is an example of clock routing. This is the command file:
   # Clock routing command file
   SOURCE NODE=clockGen PORT=clkOut STUBX=25 STUBY=0
   CHANNEL NAME=a IN=down OUT=left d1 d2 d3 d4
   CHANNEL NAME=b IN=down OUT=right d5 d6 d7 d8
   CHANNEL NAME=whole IN=left OUT=up a b

Note that there are two CHANNELs named "a" and "b" that connect the two columns of four cells. Then there is a third CHANNEL ("whole") that connects the "a" and "b" channels.

Figure 9.70

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