The Clock sheet covers power estimates of clock networks and related clock generation circuits. XPE uses explicit clocks rather than arbitrary clock frequency specification. You should define each clock using the Clocking Wizard before it can be used on any other sheet. Although it requires some setup, an explicit clock has certain advantages:
- Identification
- The unique clock name allows it to be distinguished from other clocks, particularly those with an identical frequency.
- Ease-of-use
- Modifying a clock definition propagates changes to all sheets where the clock is used.
- Consistency
- A clock's fanout is automatically accumulated from all sheets where it is used, resulting in a consistent estimation of clock network power on the Clock sheet.
The XPE Clocking wizard has a similar flow to that of the Clock IP wizard as shown in the following figure:
Figure 1. XPE Clocking Wizard
You can drive the clock using different types of sources such as:
- External
- The clock is driven from a primary input onto a global clock resource (primitive type BUFGCE).
- MMCM/XPLL/DPLL
- The MMCM/XPLL/DPLL generates one or more global clocks from an input clock
source. In most cases the source will be either External or CLKCTRL. For ease of
specification:
- It is assumed that each generated clock is driven by a BUFGCE and it is not necessary to account for these buffers separately.
- The MMCM/XPLL/DPLL power model requires only the input frequency and output frequency but not the internal divide and multiply counter values needed to generate each output.
- Clock Control Buffer (CLKCTRL)
- Use this option for instantiated global buffers: BUFGCTRL which are typically used as clock muxes, BUFGCE_DIV used as local clock dividers, and BUFGCE driven from logic resources.
- GTCLK
- Use this option for global clocks sourced from GTs (type BUFG_GT).
When you define the clock, it can be selected from a drop-down menu in the Clock column of other pages.