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Sensor driver logic

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This section describes key driver logic, or tasks, as pseudocode. These tasks include the driver's support for the following client actions:

  • Client connects
  • Client subscribes to events
  • Client unsubscribes from events
  • Client disconnects

A client connects when a desktop application invokes the ISensorCollection::GetAt method. This method returns an ISensor interface for the desired sensor. When the application releases this interface, it disconnects the client.

A client subscribes to events when a desktop application invokes the ISensorManager:SetEventSink method. When the application releases the event sink returned by this method, the client unsubscribes from events.

Abbreviations and variables

The pseudocode in this section uses the following abbreviations.

Abbreviation Explanation
CRI Current report interval (specified in milliseconds)
CS Change sensitivity (values are dependent on sensor type)
CS[] Array of change sensitivities for all data fields (for example, a 3-axis accelerometer has three entries)
LDA Location desired accuracy (applies to location only)
RS Reporting state (indicates whether eventing is enabled or disabled)
PS Power state (can be off, low, or high)

The pseudocode contains the following variables.

Variable Description
sensorID Unique identifier for a given sensor
clientID Unique identifier for a given client
flagCRI Set to True if at least one client has specified the current report interval
flagCS Set to True if at least one client has specified the change sensitivity for a device
flagLDA Set to True if at least one client has specified the location desired accuracy
deviceState Indicates the driver is connected to the device

Driver methods

A sensor driver must support both client and device initialization. The pseudocode demonstrates this using the following methods:

  • DriverClientInitialize
  • DeviceSensorInitialize

A sensor driver supports the platform's device-driver interface (DDI). The pseudocode demonstrates this using the following methods:

  • DDIOnClientConnect
  • DDIOnClientDisconnect
  • DDIOnClientSubscribeToEvents
  • DDIOnClientUnsubscribeFromEvents
  • DDIOnSetCRI
  • DDIOnSetCS
  • DDIOnSetLDA
  • DDIOnGetProperties
  • DDIOnGetDatafields
  • DDIHandleAsyncDataEvent

A sensor driver supports internal methods that handle updates to the current report interval, change sensitivity, and so on. The pseudocode demonstrates this using the following methods:

  • DriverUpdateCRI
  • DriverUpdateCS
  • DriverUpdateLDA
  • DriverUpdateSensorState
  • DriverUpdateDatafields

A sensor driver supports methods that update the sensor device. The pseudocode demonstrates this using the following methods:

  • DriverUpdateDeviceCRI
  • DriverUpdateDeviceCS
  • DriverUpdateDeviceLDA
  • DriverUpdateDeviceRS
  • DriverUpdateDevicePS

A sensor driver supports methods that interface with a device containing multiple sensors. The pseudocode demonstrates this using the following method:

  • DriverUpdateDeviceState

If a sensor driver supports HID sensors, it may support the following methods:

  • HIDSensorPollData
  • HIDSensorDeviceEvent
  • HIDSensorSetProperties
  • HIDSensorGetProperties

If a sensor driver supports HID sensors, it may support the following method for a device that contains multiple sensors:

  • HIDDeviceManagePower

If a sensor driver supports simple sensors (for example, I2C or SPI), it may support the following methods:

  • SpbSensorPollData
  • SpbSensorDeviceEvent

Driver structures and enumerations

A HID driver supports input reports. The pseudocode uses the following data structure to represent a report.

struct _inputReport
{
    reportID
    senstate
    eventType
    sensorData //this varies from sensor to sensor

} buffer, pbuffer

A sensor driver saves client data. The pseudocode uses the following data structure to save client data.

struct clientEntry
{
    clientCRI
    clientCS[]
    clientLDA
    clientSubscribed
}

A sensor driver needs to represent the device state. The pseudocode uses the following enumeration to represent the device state.

enum deviceState
{
    deviceStateDisconnected // driver is disconnected from the device
    deviceStateConnected //driver is connected to the device
}

A sensor driver needs to represent the device state. The pseudocode uses the following enumeration to represent the device state.

enum deviceState
{
    deviceStateDisconnected // driver is disconnected from the device
    deviceStateConnected //driver is connected to the device
}