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POFXCALLBACKPROCESSORHALT callback function (pepfx.h)

  • Article

The ProcessorHalt routine prepares the processor to be halted.

Syntax

POFXCALLBACKPROCESSORHALT Pofxcallbackprocessorhalt;

NTSTATUS Pofxcallbackprocessorhalt(
  [in]                ULONG Flags,
  [in, out, optional] PVOID Context,
  [in]                PPROCESSOR_HALT_ROUTINE Halt
)
{...}

Parameters

[in] Flags

Flags that indicate the properties of the idle state that the processor will enter. The Flags parameter is set to zero or to the bitwise-OR of one or more of the following flag bits.

Flag name Value Description
PROCESSOR_HALT_CACHE_FLUSH_OVERRIDE 0x01 The PEP's Halt callback routine is responsible for flushing the processor's caches. If this flag is not set, ProcessorHalt will flush the caches on entry to the processor idle state, and will invalidate the caches on exit from this state.
PROCESSOR_HALT_CACHE_COHERENT 0x02 Prepare the processor to enter an idle state in which the processor's caches will remain coherent.
PROCESSOR_HALT_CONTEXT_RETAINED 0x04 Prepare the processor to enter an idle state in which the processor's thread context will be preserved.
PROCESSOR_HALT_RETURN_NOT_SAFE 0x08 The PEP's Halt callback routine is guaranteed to not return. Set this flag if the Halt callback transitions the processor to a context-losing, power-gated state that cannot be canceled by hardware. When this flag is set, the operating system will treat a return from the Halt callback as a fatal error.
PROCESSOR_HALT_VIA_PSCI_CPU_SUSPEND 0x16

[in, out, optional] Context

A pointer to a PEP-defined processor-halt context. This pointer is passed as a parameter to the Halt callback routine. This context is opaque to the Windows power management framework (PoFx).

[in] Halt

A pointer to a PEP-implemented Halt callback routine. PoFx calls this routine after preparations to halt the processor have been completed. During this callback, the PEP is expected to transition the processor to the halted state.

Return value

ProcessorHalt returns STATUS_SUCCESS if the processor is successfully prepared to be halted. Possible error return values include the following status code.

Return value Description
STATUS_INVALID_PARAMETER
 The Halt parameter is NULL; or an invalid flag value was specified in Flags; or Flags contains an illegal combination of flag bits. For more information, see Remarks.
STATUS_UNSUCCESSFUL
 The PEP's Halt callback routine unexpectedly returned from an idle state in which the processor's hardware context was not preserved.

Remarks

This routine is implemented by the power management framework (PoFx) and is called by the platform extension plug-in (PEP). The ProcessorHalt member of the PEP_KERNEL_INFORMATION_STRUCT_V3 structure is a pointer to a ProcessorHalt routine.

Before halting the processor, the PEP calls the ProcessorHalt routine to give PoFx an opportunity to save the processor's hardware context. If necessary, ProcessorHalt saves this state internally in PoFx so that the state can later be restored when the processor exits the idle state. After preparing the processor to enter the idle state, ProcessorHalt calls the PEP's Halt callback routine to halt the processor.

As part of the PEP's handling of a PEP_NOTIFY_PPM_IDLE_EXECUTE notification, the PEP must transition the processor to the idle state that the PEP has selected. The following are the two ways to enter the processor idle state:

  • For a processor idle state in which the processor's caches remain coherent so that all system and processor state is maintained, the PEP can enter the idle state directly without first calling ProcessorHalt.
  • For a processor idle state in which the processor's caches might not remain coherent, or an idle state in which the processor hardware context is not preserved, the PEP must call ProcessorHalt before transitioning the processor to the idle state.
The following combinations of flag bits are illegal:
  • PROCESSOR_HALT_CONTEXT_RETAINED = 1 and PROCESSOR_HALT_RETURN_NOT_SAFE = 1

    The PEP's Halt callback routine must return from any state in which context is retained.

  • PROCESSOR_HALT_CACHE_FLUSH_OVERRIDE = 1 and PROCESSOR_HALT_CACHE_COHERENT = 1

    The cache-flush-override flag should be set only if entering an idle state that is not cache coherent.

  • PROCESSOR_HALT_CACHE_FLUSH_OVERRIDE = 0 and PROCESSOR_HALT_CACHE_COHERENT = 0

    The cache-flush-override flag must be set for any non-cache coherent halt.

  • PROCESSOR_HALT_CONTEXT_RETAINED = 0 and PROCESSOR_HALT_CACHE_COHERENT = 1

    Any idle states that lose processor hardware context (and therefore use the multiprocessor parking protocol to exit the idle state and return control to the operating system) are not cache-coherent states.

If the Flags parameter contains an illegal combination of flag bits, ProcessorHalt fails and returns STATUS_INVALID_PARAMETER.

The PEP can call this routine at IRQL <= HIGH_LEVEL.

Requirements

Requirement Value
Minimum supported client Supported starting with Windows 10.
Target Platform Windows
Header pepfx.h (include Pep_x.h)
IRQL <= HIGH_LEVEL

See also

PEP_KERNEL_INFORMATION_STRUCT_V3

PEP_NOTIFY_PPM_IDLE_EXECUTE