Introduction

   The USB standard explicitly encourages the separation of USB operations into various layers/levels so that relatively simple software components may manage them. Belcarra's USB Composite Device Framework carries through this program, achieving two basic objectives: centralizing basic parts of the system in re-usable components and reducing the size and complexity of both function-level and bus-level components.

     The careful partitioning of the layers in Belcarra's Composite Device Framework significantly reduces the complexity of individual functions while combining management capabilities that do not relate to specific functions and allowing easy portability to new architectures and operating systems:

Function Drivers

   a. composite

   b. class

   c. interface

Composite Core

   a. USB Function API 

   b. Composite Management API 

   c. OS Abstraction

Hardware Drivers

   a. Bus and PCD Driver library 

   b. Architecture Specific Files 

   c. Platform Specific Files and Configuration

Logically there is a 4th layer that is used for management:

Management Software

   a. usbadmin 

   b. /proc/usb-functions 

   c. /proc/trace_otg