Add documentation to the USB Class Drivers module on how to use the Host mode class drivers.

LUFA/Drivers/USB/USB.h

@@ -235,7 +235,116 @@
  *  class-specific functions.
  *
  *  \subsection SSec_ClassDriverHost Host Mode Class Drivers
+ *  Implementing a Host Mode Class Driver in a user application requires a number of steps to be followed. Firstly,
+ *  the module configuration and state structure must be added to the project source. These structures are named in a 
+ *  similar manner between classes, that of <i>USB_ClassInfo_<b>{Class Name}</b>_Host_t</i>, and are used to hold the
+ *  complete state and configuration for each class instance. Multiple class instances is where the power of the class 
+ *  drivers lie; multiple interfaces of the same class simply require more instances of the Class Driver's ClassInfo 
+ *  structure.
  *
+ *  Inside the ClassInfo structure lies two sections, a <i>Config</i> section, and a <i>State</i> section. The Config
+ *  section contains the instance's configuration parameters, and <b>must have all fields set by the user application</b>
+ *  before the class driver is used. Each Device mode Class driver typically contains a set of configuration parameters
+ *  for the endpoint size/number of the associated logical USB interface, plus any class-specific configuration parameters.
+ *
+ *  The <i>State</i> section of the ClassInfo structures are designed to be controlled by the Class Drivers only for
+ *  maintaining the Class Driver instance's state, and should not normally be set by the user application.
+ *
+ *  The following is an example of a properly initialized instance of the MIDI Class Driver structure:
+ *
+ *  \code
+ *  USB_ClassInfo_MIDI_Host_t My_MIDI_Interface =
+ *  {
+ *      .Config =
+ *          {
+ *              .DataINPipeNumber       = 1,
+ *              .DataINPipeDoubleBank   = false,
+ *              
+ *              .DataOUTPipeNumber      = 2,
+ *              .DataOUTPipeDoubleBank  = false,
+ *          },
+ *  };
+ *  \endcode
+ *
+ *  To initialize the Class driver instance, the driver's <i><b>{Class Name}</b>_Host_ConfigurePipes()</i> function
+ *  should be called in response to the host state machine entering the \ref HOST_STATE_Addressed state. This function
+ *  will return an error code from the class driver's <i><b>{Class Name}</b>_EnumerationFailure_ErrorCodes_t</i> enum
+ *  to indicate if the driver sucessfully initialized the instance and bound it to an interface in the attached device.
+ *  Like all the class driver functions, this function takes in the address of the specific instance you wish to initialize
+ *  - in this manner, multiple seperate instances of the same class type can be initialized. A fragment of a Class Driver
+ *  based Host mode application may look like the following:
+ *
+ *  \code
+ *      switch (USB_HostState)
+ *      {
+ *          case HOST_STATE_Addressed:
+ *              LEDs_SetAllLEDs(LEDMASK_USB_ENUMERATING);
+ *          
+ *              uint16_t ConfigDescriptorSize;
+ *              uint8_t  ConfigDescriptorData[512];
+ *
+ *              if (USB_Host_GetDeviceConfigDescriptor(1, &ConfigDescriptorSize, ConfigDescriptorData,
+ *                                                     sizeof(ConfigDescriptorData)) != HOST_GETCONFIG_Successful)
+ *              {
+ *                  LEDs_SetAllLEDs(LEDMASK_USB_ERROR);
+ *                  USB_HostState = HOST_STATE_WaitForDeviceRemoval;
+ *                  break;
+ *              }
+ *
+ *              if (MIDI_Host_ConfigurePipes(&My_MIDI_Interface,
+ *                                           ConfigDescriptorSize, ConfigDescriptorData) != MIDI_ENUMERROR_NoError)
+ *              {
+ *                  LEDs_SetAllLEDs(LEDMASK_USB_ERROR);
+ *                  USB_HostState = HOST_STATE_WaitForDeviceRemoval;
+ *                  break;
+ *              }
+ *
+ *              // Other state handler code here
+ *  \endcode
+ *
+ *  Note that the function also required the device's configuration descriptor so that it can determine which interface
+ *  in the device to bind to - this can be retrieved as shown in the above fragment using the
+ *  \ref USB_Host_GetDeviceConfigDescriptor() function. If the device does not implement the interface the class driver
+ *  is looking for, if all the matching interfaces are already bound to class driver instances or if an error occurs while
+ *  binding to a device interface (for example, a device endpoint bank larger that the maximum supported bank size is used)
+ *  the configuration will fail.
+ *
+ *  Once initialized, it is important to maintain the class driver's state by repeatedly calling the Class Driver's
+ *  <i><b>{Class Name}</b>_Host_USBTask()</i> function in the main program loop. The exact implementation of this
+ *  function varies between class drivers, and can be used for any internal class driver purpose to maintain each
+ *  instance. Again, this function uses the address of the instance to operate on, and thus needs to be called for each
+ *  seperate instance, just like the main USB maintenance routine \ref USB_USBTask():
+ *
+ *  \code
+ *  int main(void)
+ *  {
+ *      SetupHardware();
+ *  
+ *      LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);
+ *  
+ *      for (;;)
+ *      {
+ *          switch (USB_HostState)
+ *          {
+ *             // Host state machine handling here
+ *          } 
+ *      
+ *          MIDI_Host_USBTask(&My_Audio_Interface);
+ *          USB_USBTask();
+ *      }
+ *  }
+ *  \endcode
+ *
+ *  Each class driver may also define a set of callback functions (which are prefixed by "CALLBACK_"
+ *  in the function's name) which <b>must</b> also be added to the user application - refer to each
+ *  individual class driver's documentation for mandatory callbacks. In addition, each class driver may
+ *  also define a set of events (identifiable by their prefix of "EVENT_" in the function's name), which
+ *  the user application <b>may</b> choose to implement, or ignore if not needed.
+ *
+ *  The individual Host Mode Class Driver documentation contains more information on the non-standardized,
+ *  class-specific functions which the user application can then use on the driver instances, such as data
+ *  read and write routines. See each driver's individual documentation for more information on the
+ *  class-specific functions.
  */
  
 #ifndef __USB_H__