Proper floor-planning for PCI Express interfaces allows you to position your system for success before any actual CAD time is spent routing or re-routing the interface. A simple approach to floor-planning might involve these basic steps:

1. Create a block diagram connectivity plan for devices and/or connectors and placement studies. In addition to the actual PCI Express components, your initial diagram should include the necessary peripheral components interacting with your PCI Express components: clock sources, power supply connectors, and the like. As you apply this diagram to initial placement studies with your CAD tools, you can size up the general location on the system board of each component and assess the routing distances and areas that apply to each component or connector. The location and placement of your components is also influenced by the type of system board form factor you follow, such as ATX, micro-ATX, BTX, etc.

2. Verify connectivity rules, as explained in this chapter. Making sure that you comply with all of the specification requirements can save you from design changes down the road. Note general locations of AC capacitors and verify whether the pinouts of the PCI Express devices and components require any bowtie routing to achieve proper connectivity. Also follow the EMI and Power Delivery guidelines later in this chapter, and determine the ability to maintain good reference planes for your signals and place high power consuming devices close to their power sources.

3. Assignment of routing restrictions. You should revisit this step several...