Multiple clock domains

[wallento]

The debug subsystem should run in a different clock domain. For that there should be a clock domain crossing in each module.

Generally the crossing should take place as near to the system-side as possible, because this is better for the upcoming (cross-)triggering infrastructure.

[wallento]

Regarding the timestamp there are two options:

• Timestamp in debug domain. Pro: Identical timestamps for all modules. Con: The crossing should not buffer, but only cross the value from one domain to the other (1 position FIFO?) because otherwise the timestamp can be imprecise.
• Timestamp from module. Pro: Simple to handle (part of trace sample). Con: Timestamps need to be synchronized.