Wednesday, 2 September 2015

Real-Time Sensing on Android


    This layer enables raw H/W access. Android uses linux's input sub system (evdev) for sensor devices.
  • The input sub system is an abstraction layer b/w i/p devices and i/p handlers.
  • The i/p devices capture physical inputs and produces i/p events.
  • The i/p events then go through the i/p core and are dispatched to any subscribed handlers, which in turn make them available through the standard UNIX file interface /dev/input/eventX.
  • Thus, applications can access the raw sensors data as an i/p events by calling POSIX system calls.

    It is a user space layer that interface with the kernel.

  • It polls the i/p events from kernel (/dev/input/eventX) for reading sensor data and provides a unifying H/W interfaces for other user space process.
  • This layer also hides vendor specific details.
  • HAL is loaded into User-Space process as a shared library.

Sensor Service:

    It Uses HAL to access raw sensor data. This layer is in fact part of a system process that starts from system boot time.

Do 2 things-
  • It re formats raw H/W sensor data using application friendly data    structure.
  • It fuses reading from multiple H/W sensors to generate S/W sensors data.

Sensor manager:

    Is an Android library linked to each application at run time.
  • It Provides registration and de registration calls for app implemented event handlers.
  • Once app registers an event handler, sensor Manger's sensor thread reads sensor data from a sensor service.

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