.. _drivers:


Device Drivers
================

The Device Driver Interface
----------------------------

.. figure:: driverAPI.png
   :align: center

Device Driver Layers
----------------------------

.. figure:: driver_layers.png
   :align: center

System Call Interface
----------------------

* Functions available to application programs

* Abstract all devices (and files) to a few interfaces

* Make interfaces as similar as possible

    - Block vs character

    - Sequential vs direct access

* Device driver implements functions (one entry point per API function)

Example - UNIX Driver
-------------------------

===========  ==================================
`open`         Prepare dev for operation
`close`        No longer using the device
`ioctl`        Character dev specific info
`read`         Character dev input op
`write`        Character dev output op
`strategy`     Block dev input/output ops
`select`       Character dev check for data
`stop`         Discontinue a stream output op
===========  ==================================