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Clock Template
In order to make some Partial Reconfiguration designs work, it may be necessary to use a clock template specially constructed for this purpose. It is the starting point for each reconfigurable module illustrated in the following figure:
If a given reconfigurable module uses different clocks in each module variation, a clock template is a necessary step in the Partial Reconfiguration process. This is required in order to program the clock frames correctly. As an example, if reconfigurable module #1 is loaded into the device, the clock frames are programmed to meet the clocking needs of reconfigurable module #1, but might not accommodate the needs of reconfigurable module #2. If reconfigurable module #2 is then loaded, it will either overwrite the clock frames and simultaneously overwrite the clock programming of reconfigurable module #1, or it will not program the clock frames at all, causing the clock programming from reconfigurable module #2 to be non-existent.
The clock template programs each of the clocks used in a system, even if the clock is not used in a particular design implementation. As an example, if reconfigurable module #1 uses Clock 1 and Clock 2, and reconfigurable module #2 uses Clock 2 and Clock 3, then the clock template consists of Clocks 1, 2, and 3. Reconfigurable module #1 routes Clock 3 to a dummy flip-flop and adds the appropriate constraints so that the loadless Clock 3 is not removed. Similarly, reconfigurable module #2 ties a dummy load to the unused Clock 1.
In this way, when reconfigurable module #1 is compiled, and its bitstream writes the clock frames, the clock programming for Clocks 1, 2, and 3 will be present and both module #1 and #2 will work properly. This method is extendable; for example, if design reconfigurable module #3 also uses Clock 4, then Clock 4 is a necessary part of the clock template. The total number of different clocks in all designs must not exceed the clock resources of the device.
Because of the way modular designs are compiled, creating a clock template is not necessary if there are no clock or clock programming differences between any of the reconfigurable modules.
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