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Event communication using WFE or SEV

An external agent can use the EVENTI pin to participate in a WFE or SEV event communication with the Cortex-A53 processor. When this pin is asserted, it sends an event message to all the cores in the device. This is similar to executing a SEV instruction on one core in the cluster. This enables the external agent to signal to the cores that it has released a semaphore and that the cores can leave the WFE low-power state. The EVENTI input pin must remain HIGH for at least one CLKIN clock cycle to be visible by the cores.

The external agent can determine that at least one of the cores in the cluster has executed an SEV instruction by checking the EVENTO pin. When SEV is executed by any of the cores in the cluster, an event is signaled to all the cores in the device, and the EVENTO pin is asserted. This pin is asserted HIGH for three CLKIN clock cycles when any core in the cluster executes an SEV instruction.

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