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Architecture

A device driver consists of three separate routines:

  * Initialization Routine (INIT)
  * Device Service Routine (DSR)
  * Interrupt Service Routine (ISR)

The INIT routine initializes device hardware (for example, programmable chips) and data structures associated with the device driver.

The DSR routine is called to initiate operations on the controlled device. In most cases, the DSR sends commands to the device, returning immediately after that. The device's response could take some time and it is captured through interrupts.

The ISR routine services the interrupts coming from the device in question. Possibly the first thing to do is to query some device's control register to learn what caused the interrupt.

The ISR also performs part of the useful job. For instance, when reading from a Tape Drive, it receives the incoming bytes into a given buffer.

In source, device drivers are written in separate files with extension ".DEV".