Media Driver Guide

Purpose

This document explains the points that have to be considered when writing a media driver in an environment that uses writable data paging.

Issues to consider

The main issue to consider when writing a media device driver for a writable demand paging environment is to avoid page faults from occurring in DFCs, since this can lead to a deadlock condition between the driver and the client process.

This can be avoided using the following methods:

• Use shared chunks.

  Shared chunks are memory areas that are accessible by both kernel-side and user-side and they are never paged.

  This is the best solution for drivers that involve fast throughput such as media drivers.

• Use synchronous rather than asynchronous data transfer

  This could be done by implementing the following steps:

  1. The client requests a notification when data is available.

  2. The data arrives.

  3. The driver writes data into an internal buffer and completes the client request.

  4. The client makes a read request.

  5. The driver writes the data back to the client in the client thread context.

  This approach is easy to implement, however it requires the buffering of data.

• Use the flexible memory model

  This provides the ability for the memory to be mapped into a drive's address space as unpaged.

  This is an alternative to the use of shared chunks.

  However, this is not supported on the moving or multiple memory models.