8.1.1. Event signaling protocol

The cross-triggering system does not attempt to interpret the events that are signaled through it. Events are broadcast as a level. When an event passes across a clock domain boundary, handshaking occurs to ensure that the event lasts for at least one clock cycle in the destination clock domain.

It is not usually meaningful to count the number of cycles that an event is active for. When an event is signaled between clock domains, it might be active for a different number of cycles in the new domain. For example, an event which is active for one cycle in one clock domain might be active for several cycles if connected to a slower clock domain. Therefore for most event types, components use the rising edge of a trigger output signal to indicate an event.

In usage models that count events passed through the cross-triggering system, events that occur close together might be merged into a single event with a single rising edge when passed to another clock domain. This might occur even when passing from a slower clock domain to a faster clock domain, because of the delay associated with synchronizing between two clock domains.

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