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QNX Hypervisor and QNX Hypervisor for Safety
The QNX Hypervisor and QNX Hypervisor for Safety products allow you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
Virtual Device Developer's API Reference
The Virtual Device Developer's API Reference presents the QNX hypervisor public virtual device (vdev) API. It is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
guest.h
Controls for manipulating a guest system
guest_clock_start()
Start the flow of billable vCPU time

QNX Momentics IDE User's Guide
This User's Guide describes version 8.0 of the Integrated Development Environment (IDE) that's part of the QNX Tool Suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX software in Amazon Web Services (AWS) and Microsoft Azure (Azure).
QNX Toolkit for Visual Studio Code
This User's Guide describes the QNX^® Toolkit for Visual Studio Code. The guide introduces you to the QNX Toolkit by explaining the QNX development environment and how to build, run, and debug your QNX^® Operating System (OS) applications and systems.
QNX Hypervisor and QNX Hypervisor for Safety
The QNX Hypervisor and QNX Hypervisor for Safety products allow you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
- User's Guide
  This User's Guide explains the QNX hypervisor architecture and provides instructions for installing and running a QNX hypervisor system, changing system components and configuration, and using hypervisor features such as virtual devices (vdevs).
- Virtual Device Developer's Guide
  The Virtual Device Developer's Guide is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
- Virtual Device Developer's API Reference
  The Virtual Device Developer's API Reference presents the QNX hypervisor public virtual device (vdev) API. It is intended for use by developers writing virtual devices (vdevs) in a QNX hypervisor system.
  - Function Safety
    This section provides an overview of the restrictions that may apply when using the functions in this API.
  - aarch64/vmid.h
    Functions to access a guest's VMID (ARM)
  - abi.h
    Application binary interface (ABI) information
  - cdev.h
    Support routines for virtual character devices
  - firmware.h
    Functions for working with the firmware components of the VM presented to the guest
  - gasp.h
    Definitions and functions for working in guest address spaces
  - guest.h
    Controls for manipulating a guest system
    - Definitions in guest.h
      Preprocessor macro definitions for the guest.h header file
    - guest_button_register()
      Mark the system as having a power state handler vdev
    - guest_buttons_type_t
      Data type representing console buttons
    - guest_clock_start()
      Start the flow of billable vCPU time
    - guest_clock_stop()
      Stop the flow of billable vCPU time
    - guest_cpu_access_flags_t
      Flags for vCPU state read/write requests
    - guest_cpu_read()
      Read data from a guest CPU (i.e., a vCPU) or the guest address space
    - guest_cpu_write()
      Write data to a guest CPU (i.e., a vCPU) or the guest address space
    - guest_instr_callback_func_t
      Prototype for callback function for handling guest instructions
    - guest_instr_register()
      Register a callback function to invoke when the guest executes a particular instruction
    - guest_instr_type_t
      Data type representing guest instructions for which you can get a callback
    - guest_intr_assign()
      Assign a source to an interrupt
    - guest_intr_assign_auto()
      Automically pick an interrupt and assign it to the guest
    - guest_intr_from_conf_str()
      Parse a guest interrupt specification in the VM configuration format
    - guest_intr_get_level()
      Return the global level for an interrupt line
    - guest_intr_signal()
      Assert or de-assert an interrupt request to a PIC or guest CPU
    - guest_intr_to_string()
      Produce a human-readable string to describe the given guest interrupt
    - guest_memory_filter_kind
      Kinds of memory filters
    - guest_msi_ctlr_create()
      Create a Message Signaled Interrupt (MSI) controller
    - guest_msi_decode_table_cb_t
      Function prototype for the callback to decode a firmware table
    - guest_msi_deliver_cb_t
      Function prototype for the callback to deliver a Message Signaled Interrupt (MSI)
    - guest_msi_register_range()
      Add a memory address range to be decoded by a controller
    - guest_msi_signal()
      Send an MSI to a guest
    - guest_num_cpus()
      Get the number of virtual CPUs in the virtual machine
    - guest_pic_notify()
      Handle an interrupt event that has occurred on an interrupt line that PIC is aware of
    - guest_pic_set_num_pins()
      Set the size of the PIC vdev pin_info array
    - guest_power_state_callback_func_t
      Function prototype for power state callback
    - guest_power_state_cmd_t
      Data type for guest CPU power states
    - guest_power_state_current()
      Return the current power state of the guest system
    - guest_power_state_notify_create()
      Create a structure to hold a power state change callback
    - guest_power_state_notify_delete()
      Remove a power state notification structure
    - guest_power_state_notify_register()
      Set the characteristics of a power state notification structure
    - guest_register_memory_filter()
      Register a guest memory filter
    - guest_terminate()
      Terminate the execution of a guest
    - guest_termination_cause_t
      Data type representing cause of guest termination
    - guest_timer_create()
      Create a guest system timer
    - guest_timer_data
      Structure for timer information
    - guest_timer_notify()
      Request notification when a guest timer passes a given point
    - guest_timer_state()
      Get state information for a guest timer
    - guest_write_all_ones()
      Write a series of ones to a guest CPU (i.e., a vCPU)
    - guest_write_core_file()
      Write out the guest core file
  - hpci.h
    Host PCI interface for vdevs
  - hw_pci.h
    PCI support for vdevs
  - log.h
    Controls for logging messages
  - types.h
    vdev API base types
  - utils.h
    Miscellaneous utility functions
  - vdev-core.h
    Definitions and functions that support vdev control functions and callbacks
  - vio.h
    Definitions and functions for working with VIRTIO vdevs
  - vpci.h
    Controls for virtual PCI (vPCI) devices
  - wdog.h
    Constants, data types, and functions to support virtual watchdog devices
  - x86_64/apic.h
    Definitions for the virtual APIC bus (x86)
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation, explains how to obtain technical support, and provides some information about licensing.

guest_clock_start()

Start the flow of billable vCPU time

Synopsis:

#include <qvm/guest.h>

void guest_clock_start(void)

Description:

This function can be called by a vdev callback to start the flow of billable vCPU time. A vdev should consider its execution time as billable if it is performing an operation that is not emulation overhead and can be counted towards stolen time. This latter term refers to the time that the calling vCPU can't run on a physical CPU because it was preempted by another thread in the hypervisor host. Here, the calling vCPU means the vCPU that's executing guest code that prompted the guest exit that made the vdev code run. For information about stolen time, read the Time section in the QNX hypervisor User's Guide.

Page updated: March 14, 2026