chip floor planning tools
some important hints to remember when using a floorplanning tool:
• Initially, all pads at the top level are assigned to be connected to a single
layer. This constraint affects the router in its ability to optimize the connections
to the pads. In some cases the pads can be assigned to two layers, which
gives the router more freedom. In the case of many available layers ,
the assignment of pads to routing layers is best left to the layout
designer and assigned manually. There may be dedicated layers for some
ports that need to be assigned, such as power supplies and clocks.
• Block pins may have to be manually assigned to the correct layer as in the
previous case.
• Inserting spare logic and signals is tricky. Typically, the netlist of a design
does not contain spare elements, so these elements need to be inserted manually
as well. The person using the tool should learn how to “massage” the
netlist by introducing “fictional” lines and pins, enlarging blocks for spare
logic, and adding dummy blocks that will be used for spare logic. Proper
placement of the spare elements is also necessary to ensure that the spare
lines are close to the spare logic so they can be used easily.
• Blocks that are subject to change should be placed strategically where there
might be extra space for the block to grow in size.