Acknowledge Mechanism - 2020.2 English

Zynq UltraScale+ MPSoC Software Developer Guide (UG1137)

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2020.2 English

The Zynq UltraScale+ MPSoC power management framework (PMF) supports blocking and non-blocking acknowledges. In most API calls that offer an acknowledge argument, the caller can choose one of the following three acknowledge options:

  • REQUEST_ACK_NO: No acknowledge requested
  • REQUEST_ACK_BLOCKING: Blocking acknowledge requested
  • REQUEST_ACK_NON_BLOCKING: Non-blocking acknowledge using callback requested

Multiple power management API calls are serialized because each processor unit (PU) uses a single IPI channel for the API calls. After one request is sent to the power management controller, the next one can be issued only after the power management controller has completed servicing the first one. Therefore, no matter which acknowledge mechanism is used, the caller can be blocked when issuing subsequent requests.

No Acknowledge

If no acknowledge is requested (REQUEST_ACK_NO), the power management controller processes the request without returning an acknowledge to the caller, otherwise an acknowledgment is sent.

Blocking Acknowledge

After initiating a PM request with the (REQUEST_ACK_BLOCKING) specified, a caller remains blocked as long as the power management controller does not provide the acknowledgment.

The platform management unit (PMU) writes the acknowledge values into the response portion of the IPI buffer before it clears the IPI interrupt. The caller reads the acknowledge values from the IPI buffer after the IPI observation register shows that the interrupt is cleared, which is when PMU has completed servicing the issued IPI. The IPI for the PU is disabled until the PMU is ready to handle the next request.

Non-Blocking Acknowledge

After initiating a PM request with the (REQUEST_ACK_NON_BLOCKING) specified, a caller does not wait for the platform management unit (PMU) to process that request. Moreover, the caller is free to perform some other activities while waiting for the acknowledge from the PMU.

After the PMU completes servicing the request, it writes the acknowledge values into the IPI buffer. Next, the PMU triggers the IPI to the caller PU to interrupt its activities, and to inform it about the sent acknowledge.

Non-blocking acknowledges are implemented using a callback function that is implemented by the calling PU, see XPm_NotifyCb Callback.

For more information about XPm_NotifyCb, see XilPM Library in the OS and Libraries Document Collection (UG643).