Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public

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8.6.2.4. Reset Assertion Sequence

The following diagram shows the reset assertion sequence, which can be entered from either the HPS idle sequence or the wait for reset requests to de-assert sequence.

Figure 273. Reset Assertion Sequence

Upon entering the assert boot mode request step, the reset manager state machine takes a snapshot of all pending reset requests. Upon entering the assert cold or warm reset step, the state machine asserts the reset signals associated with the highest priority reset request in the snapshot that it took. This behavior allows a newer cold reset request to take priority over an older warm reset request, so that a warm reset request can start the HPS idle sequence, but a later cold reset request is actually taken during this sequence.

When entering the reset assertion sequence from the wait for reset requests to de-assert sequence, it is necessary to once again assert the serial controller reset so that the HPS is in the same state as if entered from the HPS idle sequence. This is because the serial controller reset is asserted at the start of the HPS idle sequence, which has been skipped in this case. Once the state machine completes the reset assertion sequence, it proceeds to the wait for reset requests to de-assert stage. Only a POR causes the sequence of steps shown above to be aborted.