/** \file
 *
 *  This file contains special DoxyGen information for the generation of the main page and other special
 *  documentation pages. It is not a project source file.
 */

/** \page Page_Migration Migrating from Older Versions
 *
 *  Below is migration information for updating existing projects based on previous versions of the LUFA library
 *  to the next version released. It does not indicate all new additions to the library in each version change, only
 *  areas relevant to making older projects compatible with the API changes of each new release.
 *
 *  \section Sec_Migration111009 Migrating from 110528 to 111009
 *  <b>Non-USB Library Components</b>
 *    - The \c JTAG_DEBUG_ASSERT() macro has been renamed \ref JTAG_ASSERT() to be consistent with \ref STDOUT_ASSERT().
 *
 *  <b>USB Core</b>
 *    - By default, unordered Endpoint and Pipe configuration is now allowed once again, via the previous workaround of
 *      reconfiguring all Endpoints/Pipes in order each time a new Endpoint/Pipe is created. To minimize the compiled program
 *      size, the new \c ORDERED_EP_CONFIG compile time option may be defined in the project makefile to restrict the ordering
 *      in exchange for a smaller compiled binary size.
 *    - The previous \c F_CLOCK symbol, required in the project makefile, has been renamed to \c F_USB. This is due to the previous name
 *      being far too generic for use in future architecture ports, where multiple clock domains are used.
 *
 *  <b>Device Mode</b>
 *    - The Endpoint stream functions now all require a \c BytesProcessed parameter instead of the previous callback parameter.
 *      This should be set to \c NULL to retain previous behaviour of the functions, or point to a location where the number of bytes
 *      processed in the current transaction can be stored. If the \c BytesProcessed parameter is non \c NULL, each time the endpoint
 *      bank becomes full and the packet is sent, the routine will exit with the new \ref ENDPOINT_RWSTREAM_IncompleteTransfer
 *      error code to allow the user application to determine when to send the next chunk of data.
 *    - The \ref CDC_Device_SendString() function now expects a null terminated string instead of an explicit length. Existing code
 *      should use the new \ref CDC_Device_SendData() function, or remove the length parameter from the function call.
 *    - The \c Endpoint_ResetFIFO() function has been renamed to \ref Endpoint_ResetEndpoint(), to make the API function names more
 *      consistent. Existing applications using the old function name should simply replace it with a call to the new function name.
 *    - The \c Endpoint_*_Byte() functions have been renamed Endpoint_*_8() to ensure they are correct across all architectures. Existing
 *      code using these functions should replace the previous function names with the new function names.
 *    - The \c Endpoint_*_Word() functions have been renamed Endpoint_*_16() to ensure they are correct across all architectures. Existing
 *      code using these functions should replace the previous function names with the new function names.
 *    - The \c Endpoint_*_DWord() functions have been renamed Endpoint_*_32() to ensure they are correct across all architectures. Existing
 *      code using these functions should replace the previous function names with the new function names.
 *    - The Device mode RNDIS class driver no longer stores the incoming and outgoing packets in the class driver instance; the user is
 *      now expected to manually define a storage location for the packet data. Packets must now be sent and received manually via a call
 *      to \ref RNDIS_Device_ReadPacket() and/or \ref RNDIS_Device_SendPacket().
 *    - The definition of the Audio class \ref USB_Audio_Descriptor_Format_t has been altered, to remove the fixed singular
 *      audio sample rate in the descriptor definition, and to rename the \c SampleFrequencyType to the more appropriate
 *      \c TotalDiscreteSampleRates. Existing applications will need to add an array of \ref USB_Audio_SampleFreq_t elements
 *      immediately following any \ref USB_Audio_Descriptor_Format_t descriptors, and insert the appropriate sampling rates
 *      supported by the device, as well as rename the descriptor elements to match the updated element names.
 *    - The device mode Audio class driver now requires a new user application callback, \ref CALLBACK_Audio_Device_GetSetEndpointProperty().
 *      Existing applications must implement this new callback, however if multiple sample rates or pitch control is not used,
 *      this function may be hard-coded to always return false for previous behaviour to be retained.
 *    - The \c USB_ConfigurationNumber, \c USB_RemoteWakeupEnabled and \c USB_CurrentlySelfPowered globals have been renamed to
 *      \ref USB_Device_ConfigurationNumber, \ref USB_Device_RemoteWakeupEnabled and \ref USB_Device_CurrentlySelfPowered to clearly indicate
 *      the USB mode they relate to. Existing applications using these variables should rename all references to the previous names.
 *    - The \c ENDPOINT_DESCRIPTOR_DIR_IN and \c ENDPOINT_DESCRIPTOR_DIR_OUT macros have now been replaced by \ref ENDPOINT_DIR_IN and
 *      \ref ENDPOINT_DIR_OUT to improve code clarity.
 *    - The \ref HID_DESCRIPTOR_JOYSTICK() macro now takes an additional (first) parameter indicating the number of axis in the joystick.
 *
 *  <b>Host Mode</b>
 *    - The Pipe stream functions now all require a \c BytesProcessed parameter instead of the previous callback parameter.
 *      This should be set to \c NULL to retain previous behaviour of the functions, or point to a location where the number of bytes
 *      processed in the current transaction can be stored. If the BytesProcessed parameter is non \c NULL, each time the pipe
 *      bank becomes full and the packet is sent, the routine will exit with the new \ref PIPE_RWSTREAM_IncompleteTransfer
 *      error code to allow the user application to determine when to send the next chunk of data.
 *    - The \ref PRNT_Host_SendString() and \ref CDC_Host_SendString() functions now expect a null terminated string instead of an explicit
 *      length. Existing code should use the new \ref PRNT_Host_SendData() and \ref CDC_Host_SendData() functions, or remove the
 *      length parameter from the function call.
 *    - The \c Pipe_ClearErrorFlags() function has been removed, as the pipe error flags are now automatically cleared when the
 *      \ref Pipe_ClearError() function is called.
 *    - The \c Pipe_*_Byte() functions have been renamed Pipe_*_8() to ensure they are correct across all architectures. Existing code using
 *      these functions should replace the previous function names with the new function names.
 *    - The \c Pipe_*_Word() functions have been renamed Pipe_*_16() to ensure they are correct across all architectures. Existing code using
 *      these functions should replace the previous function names with the new function names.
 *    - The \c Pipe_*_DWord() functions have been renamed Pipe_*_32() to ensure they are correct across all architectures. Existing code using
 *      these functions should replace the previous function names with the new function names.
 *    - The \c USB_Host_ClearPipeStall() function has been renamed to USB_Host_ClearEndpointStall(), as it operates on a full endpoing address
 *      within the attached device and not a pipe within the host. Existing code using the old function name should update the function calls and
 *      check for correct usage.
 *
 *  \section Sec_Migration101122 Migrating from 100807 to 101122
 *  <b>USB Core</b>
 *    - A new USB driver source file, \c Drivers/USB/HighLevel/EndpointStream.c now exists. This source file should be added
 *      to all project makefiles using the USB driver of LUFA, or the makefile should be updated to use the new module source
 *      variables.
 *    - A new USB driver source file, \c Drivers/USB/HighLevel/PipeStream.c now exists. This source file should be added to all
 *      project makefiles using the USB driver of LUFA, or the makefile should be updated to use the new module source variables.
 *    - The \c EVENT_USB_InitFailure() event has been removed, as the \ref USB_Init() function will no longer fail; if not USB mode is
 *      specified, the controller will default to UID selection mode.
 *    - The USB mode specifier constants have been moved into a new enum and renamed. Existing projects should use the equivalent
 *      value in the new \ref USB_Modes_t enum.
 *    - All class driver headers are now included as part of the standard \c LUFA/Drivers/USB/USB.h master dispatch header, and should
 *      no longer be included separately. Class driver module source files must still be added as a separate module in the project's
 *      makefile if used.
 *
 *  <b>Device Mode</b>
 *    - Endpoints MUST be allocated in ascending order to ensure that bank corruption does not occur. Ensure that your user application
 *      allocated endpoints in ascending order - or if your application uses the USB device mode class drivers, ensure that each instance's
 *      endpoint indexes are not overlapped with other interface's endpoints.
 *    - The signature for the \ref CALLBACK_USB_GetDescriptor() callback has changed, the \c void** \c const \c DescriptorAddress parameter is
 *      now \c const \c void** \c const \c DescriptorAddress. Existing applications should update their callback signatures to match this, and
 *      eliminate any casting of descriptor pointers to a non \c const pointer.
 *    - The names of the class specific descriptor type defines in the USB Class drivers have changed - refer to the driver documentation
 *      for each class driver for the new class specific descriptor type names.
 *    - The \c ENDPOINT_DOUBLEBANK_SUPPORTED() macro is has been renamed \ref ENDPOINT_BANKS_SUPPORTED() and now returns the total number of
 *      banks supported by the given endpoint. Existing code should switch to the new naming scheme, and test that the return value of the
 *      macro is equal to or greater than 2 to regain the previous functionality.
 *    - The \c EVENT_USB_Device_UnhandledControlRequest() event is now named \ref EVENT_USB_Device_ControlRequest() and fires before (not after)
 *      the internal library event handlers. Existing code should rename the event handlers in the user application to match the new event
 *      name, and should ensure that the new execution order does not affect the application's operation.
 *
 *  <b>Host Mode</b>
 *    - Pipes MUST be allocated in ascending order to ensure that bank corruption does not occur. Ensure that your user application
 *      allocated pipes in ascending order - or if your application uses the USB host mode class drivers, ensure that each instance's
 *      pipe indexes are not overlapped with other interface's pipes.
 *    - The \c PRNT_Host_SendData() function has been renamed to \ref PRNT_Host_SendString(). Existing applications should simply
 *      replace all references to the obsolete function name with the new function name.
 *    - The names of the class specific descriptor type defines in the USB Class drivers have changed - refer to the driver documentation
 *      for each class driver for the new class specific descriptor type names.
 *    - The Still Image Host class' function prefix has been changed from \c SImage_ to  \c SI_, to remain consistent with the rest of the
 *      driver's enums, type defines and constants.
 *
 *  \section Sec_Migration100807 Migrating from 100513 to 100807
 *
 *  <b>Non-USB Library Components</b>
 *    - The Dataflash board driver stub file has changed, as dataflash functions previously located in the internal
 *      Dataflash driver of the library have now been moved to the individual board files. Existing drivers can
 *      copy-paste the new functions from the board Dataflash stub driver.
 *
 *  <b>USB Core</b>
 *    - A new USB driver source file, \c Drivers/USB/LowLevel/Device.c now exists. This source file should be added to all project
 *      makefiles using the USB driver of LUFA, or the makefile should be updated to use the new module source variables.
 *    - The \c Drivers/USB/LowLevel/DevChapter9.c source file has moved to \c Drivers/USB/HighLevel/DeviceStandardReq.c - this should
 *      be updated in all project makefiles, or the makefile should be updated to use the new module source variables.
 *    - The \c Drivers/USB/LowLevel/HostChapter9.h source file has moved to \c Drivers/USB/HighLevel/HostStandardReq.c - this should
 *      be updated in all project makefiles, or the makefile should be updated to use the new module source variables.
 *    - The \c Drivers/USB/LowLevel/LowLevel.c source file has moved to \c Drivers/LowLevel/USBController.c - this should be updated
 *      in all project makefiles, or the makefile should be updated to use the new module source variables.
 *
 *  <b>Device Mode</b>
 *    - The \c USB_Device_IsRemoteWakeupSent() macro has been removed, as the remote wakeup request is now fully handled by the
 *      enhanced \ref USB_Device_SendRemoteWakeup() function. Existing code may now discard any checks to \c USB_Device_IsRemoteWakeupSent().
 *    - The \c USB_Device_IsUSBSuspended() macro has been removed, as it is obsolete. Existing code should compare \ref USB_DeviceState
 *      to see if it the device is in the \ref DEVICE_STATE_Suspended state instead.
 *    - The \ref CDC_Device_ReceiveByte() function has changed, and now returns a signed 16-bit integer, with -1 indicating no data was
 *      received. This allows for more efficient coding, as a call to \ref CDC_Device_BytesReceived() is no longer needed if the exact
 *      number of queued bytes received is not needed.
 *
 *  <b>Host Mode</b>
 *    - The \ref CDC_Host_ReceiveByte() function has changed, and now returns a signed 16-bit integer, with -1 indicating no data was
 *      received. This allows for more efficient coding, as a call to \ref CDC_Host_BytesReceived() is no longer needed if the exact
 *      number of queued bytes received is not needed.
 *    - The \ref CDC_Host_USBTask() now calls \ref CDC_Host_Flush() automatically, flushing any queued data to the attached device. Manual
 *      flushing of the interface is no longer needed if the flushes should be in sync with calls to \ref CDC_Host_USBTask().
 *
 *  \section Sec_Migration100513 Migrating from 100219 to 100513
 *
 *  <b>Non-USB Library Components</b>
 *    - The \ref TWI_StartTransmission() function now takes in a timeout period, expressed in milliseconds, within which the addressed
 *      device must respond or the function will abort.
 *
 *  <b>Device Mode</b>
 *    - The \ref USB_Init() function no longer calls \c sei() to enable global interrupts, as the user application may need
 *      to perform other initialization before it is ready to handle global interrupts. The user application is now responsible
 *      for enabling global interrupts before or shortly after calling \ref USB_Init() to ensure that the enumeration process
 *      functions correctly.
 *    - The \c USBInterrupt.c USB driver source file has been relocated from \c LUFA/Drivers/USB/HighLevel/ to \c LUFA/Drivers/USB/LowLevel.
 *      Projects must update their makefile SRC values accordingly.
 *    - The HID Device Class driver's function signature for the \ref CALLBACK_HID_Device_ProcessHIDReport() function has been changed, to
 *      allow for a new \c ReportType parameter. This new parameter must be added in all user applications using the Device mode HID Class
 *      Driver, but may be ignored unless Host-to-Device FEATURE HID reports are used.
 *
 *  <b>Host Mode</b>
 *    - The \ref USB_Init() function no longer calls \c sei() to enable global interrupts, as the user application may need
 *      to perform other initialization before it is ready to handle global interrupts. The user application is now responsible
 *      for enabling global interrupts before or shortly after calling \ref USB_Init() to ensure that the enumeration process
 *      functions correctly.
 *    - The \c USBInterrupt.c USB driver source file has been relocated from \c LUFA/Drivers/USB/HighLevel/ to \c LUFA/Drivers/USB/LowLevel.
 *      Projects must update their makefile \c SRC values accordingly.
 *    - The HID Host Class driver's function signature for the \ref HID_Host_SendReportByID() function has been changed, to allow for a new
 *      ReportType parameter. Existing calls to this function should substitute \c REPORT_ITEM_TYPE_Out as this parameter's value.
 *
 *  \section Sec_Migration100219 Migrating from 091223 to 100219
 *
 *  <b>Non-USB Library Components</b>
 *    - Due to some ADC channels not being identical to their ADC MUX selection masks for single-ended conversions on some AVR models,
 *      the ADC driver now has explicit masks for each of the standard ADC channels (see \ref Group_ADC). These masks should be used
 *      when calling the ADC functions to ensure proper operation across all AVR models. Note that the \ref ADC_SetupChannel() function
 *      is an exception, and should always be called with a channel number rather than a channel mask.
 *
 *  <b>Host Mode</b>
 *    - The MIDI Host Class driver send and receive routines now operate on packed events, where multiple MIDI events may be
 *      packed into a single USB packet. This means that the sending of MIDI events will now be delayed until the MIDI send
 *      pipe bank is full. To override this new behaviour and revert to the previous behaviour, the user application may manually
 *      flush the queued event(s) to the device by calling \ref MIDI_Host_Flush().
 *    - The \ref Pipe_IsEndpointBound() function now takes the endpoint's direction into account, by checking if the MSB of the endpoint's address
 *      is set to denote IN endpoints. If the previous functionality where the direction is to be discounted is required, mask the endpoint
 *      address against the \ref PIPE_EPNUM_MASK token before calling \ref Pipe_IsEndpointBound().
 *
 *  <b>Device Mode</b>
 *    - The MIDI Device Class driver send and receive routines now operate on packed events, where multiple MIDI events may be
 *      packed into a single USB packet. This means that the sending of MIDI events will now be delayed until the MIDI send
 *      endpoint bank is full. To override this new behaviour and revert to the previous behaviour, the user application may manually
 *      flush the queued event(s) to the host by calling \ref MIDI_Device_Flush().
 *
 *  \section Sec_Migration091223 Migrating from 091122 to 091223
 *
 *  <b>Host Mode</b>
 *    - The Still Image Host Class driver \ref SI_Host_USBTask() and \ref SI_Host_ConfigurePipes() functions were misnamed, and are
 *      now named \c SImage_Host_USBTask() and \c SImage_Host_ConfigurePipes() respectively.
 *    - The \c HOST_SENDCONTROL_DeviceDisconnect enum value has been renamed to \ref HOST_SENDCONTROL_DeviceDisconnected to be in
 *      line with the rest of the library error codes.
 *    - The HID Parser item usages no longer contain separate minimum and maximum values, as this was a violation of the HID
 *      specification. Instead, the values are distributed evenly across each item as its usage value, to ensure that all items
 *      can be distinguished from one-another.
 *
 *  <b>Device Mode</b>
 *    - The \ref CALLBACK_HID_Device_CreateHIDReport() HID Device Class driver callback now has a new \c ReportType parameter to
 *      indicate the report type to generate. Existing applications may simply add and ignore this additional parameter.
 *
 *  \section Sec_Migration091122 Migrating from 090924 to 091122
 *
 *  <b>Host Mode</b>
 *    - The \c HID_PARSE_UsageStackOverflow HID parser error constant is now named \ref HID_PARSE_UsageListOverflow
 *    - The \ref CALLBACK_HIDParser_FilterHIDReportItem() HID Parser callback now passes a complete \ref HID_ReportItem_t to the
 *      user application, instead of just its attributes.
 *    - The \c USB_GetDeviceConfigDescriptor() function was incorrectly named and is now called \ref USB_Host_GetDeviceConfigDescriptor().
 *
 *  \section Sec_Migration090924 Migrating from 090810 to 090924
 *
 *  <b>Non-USB Library Components</b>
 *    - The \c ADC_Off() function has been renamed to \c ADC_ShutDown() to be consistent with the rest of the library.
 *    - The \ref SPI_Init() routine's parameters have changed, so that the clock polarity and data sampling modes can be set. See
 *      the \ref SPI_Init() function documentation for more details
 *    - The \ref Dataflash_Init() routine no longer initializes the SPI bus - the SPI bus should be initialized manually via a
 *      call to \ref SPI_Init() before using the Dataflash driver
 *
 *  <b>Host Mode</b>
 *    - The \c USB_GetDeviceConfigDescriptor() function's parameters and behaviour has changed; the user is required to
 *      preallocate the largest allowable buffer, and pass the size of the buffer to the function. This allows for a single
 *      call to the function to retrieve, size check and validate the Configuration Descriptor rather than having the user
 *      application perform these intermediary steps.
 *    - The HID report parser now requires a mandatory callback in the user code, to filter only the items the application
 *      is interested in into the processed HID report item structure to save RAM. See \ref CALLBACK_HIDParser_FilterHIDReportItem().
 *    - The HID report parser now always parses FEATURE and always ignores constant-data items - the \c HID_ENABLE_FEATURE_PROCESSING
 *      and \c HID_INCLUDE_CONSTANT_DATA_ITEMS compile time tokens now have no effect.
 *    - The \c USE_NONSTANDARD_DESCRIPTOR_NAMES compile time token has been removed - there are now separate \c USB_Descriptor_*
 *      and \c USB_StdDescriptor_* structures for both the LUFA and standardized element naming conventions so that both may be used in
 *      the one project. For existing projects using the standardized names, change all code to use the \c USB_StdDescriptor_* variants.
 *
 *  <b>Device Mode</b>
 *    - The \c USE_NONSTANDARD_DESCRIPTOR_NAMES compile time token has been removed - there are now separate \c USB_Descriptor_*
 *      and \c USB_StdDescriptor_* structures for both the LUFA and standardized element naming conventions so that both may be used in
 *      the one project. For existing projects using the standardized names, change all code to use the \c USB_StdDescriptor_* variants.
 *
 *  \section Sec_Migration090810 Migrating from 090605 to 090810
 *
 *  <b>All</b>
 *    - The "Simple Scheduler" has been <i>deprecated</i>, as it was little more than an abstracted loop and caused much confusion.
 *      User applications using the scheduler should switch to regular loops instead. The scheduler code will be removed in a future
 *      release.
 *    - The "Dynamic Memory Block Allocator" has been removed, as it was unused in (and unrelated to) the LUFA library and never
 *      used in user applications.
 *
 *  <b>Non-USB Library Components</b>
 *    - The \c ATTR_NOINLINE function attribute macro has been renamed to \ref ATTR_NO_INLINE to be in line with the rest of the function attribute
 *      macro names.
 *
 *  <b>Library Demos</b>
 *    - Most demos now have a corresponding Class Driver implementation, which uses the new internal library class drivers for the standard
 *      USB classes. This allows for more rapid device and host development, and so should be used in preference to the low level APIs where
 *      possible so that fixes to the class drivers propagate to all applications which use them automatically with each new LUFA release.
 *
 *  <b>Host Mode</b>
 *    - The \c HIDParser.c module has moved from \c LUFA/Drivers/USB/Class/ to \c LUFA/Drivers/USB/Class/Host/.
 *    - The \c USB_GetDeviceConfigDescriptor() function now requires the desired configuration index within the device as its first
 *      parameter, to add support for multi-configuration devices. Existing code should use a configuration index of 1 to indicate the
 *      first configuration descriptor within the device.
 *    - The non-standard "Ready" host state has been removed. Existing \ref HOST_STATE_Configured code should be moved to the end of
 *      the existing \ref HOST_STATE_Addressed state, and the existing HOST_STATE_Ready state code should be moved to the \ref HOST_STATE_Configured
 *      state.
 *    - The \c USB_IsConnected global has been removed, as it is too vague for general use. Test \ref USB_HostState explicitly to ensure the host is
 *      in the desired state instead.
 *    - The USB event names have been changed and their firing conditions changed to properly separate out Host mode events from Device mode
 *      events. See the \ref Group_Events page for details on the new event names and firing conditions.
 *
 *  <b>Device Mode</b>
 *    - The \ref CALLBACK_USB_GetDescriptor() function now takes an extra parameter to specify the descriptor's memory space so that
 *      descriptors in mixed memory spaces can be used. The previous functionality can be returned by defining the \c USE_FLASH_DESCRIPTORS
 *      token in the project makefile to fix all descriptors into FLASH space and remove the extra function parameter.
 *    - The \c USB_IsSuspended global has been removed - test \ref USB_DeviceState against \ref DEVICE_STATE_Suspended instead.
 *    - The \c USB_IsConnected global has been removed, as it is too vague for general use. Test \ref USB_DeviceState explicitly to ensure the device
 *      is in the desired state instead.
 *    - The VBUS events have been removed, as they are already exposed to the user via the \c USB_Connect and \c USB_Disconnect events.
 *    - The USB event names have been changed and their firing conditions changed to properly separate out Host mode events from Device mode
 *      events. See the \ref Group_Events page for details on the new event names and firing conditions.
 *
 *  \section Sec_Migration090605 Migrating from 090510 to 090605
 *
 *  <b>Device Mode</b>
 *    - Support for non-control data endpoint interrupts has been dropped due to many issues in the implementation. All existing
 *      projects using interrupts on non-control endpoints should switch to polling. For control interrupts, the library can
 *      manage the control endpoint via interrupts automatically by compiling with the \c INTERRUPT_CONTROL_ENDPOINT token defined.
 *    - The \c DESCRIPTOR_ADDRESS() macro has been removed. User applications should use normal casts to obtain a descriptor's memory
 *      address.
 *    - The library events system has been rewritten, so that all macros have been removed to allow for clearer user code. See
 *      \ref Group_Events for new API details.
 *    - The \c STREAM_CALLBACK() macro has been removed. User applications should replace all instances of the macro with regular
 *      function signatures of a function accepting no arguments and returning a \c uint8_t value.
 *    - The \c Event_DeviceError() event no longer exists, as its sole caller (unlinked \c USB_GetDescriptor() function) now produces a
 *      compilation error rather than a runtime error. The \c StdDescriptors.c file no longer exists as a result, and should be removed
 *      from project makefiles.
 *    - The \c USB_GetDescriptor() function has been renamed to \ref CALLBACK_USB_GetDescriptor() to be in line with the new \c CALLBACK_
 *      function prefixes for functions which <i>must</i> be implemented in the user application.
 *
 *  <b>Host Mode</b>
 *    - Support for non-control data pipe interrupts has been dropped due to many issues in the implementation. All existing
 *      projects using interrupts on non-control pipes should switch to polling.
 *    - The library events system has been rewritten, so that all macros have been removed to allow for clearer user code. See
 *      \ref Group_Events for new API details.
 *    - The \c STREAM_CALLBACK() macro has been removed. User applications should replace all instances of the macro with regular
 *      function signatures of a function accepting no arguments and returning a \c uint8_t value.
 *    - The \c DESCRIPTOR_COMPARATOR() macro has been removed. User applications should replace all instances of the macro with
 *      regular function signatures of a function accepting a void pointer to the descriptor to test, and returning a \c uint8_t value.
 *
 *  \section Sec_Migration090510 Migrating from 090401 to 090510
 *
 *  <b>All</b>
 *    - The \c ButtLoadTag.h header has been removed, as it was never used for its intended purpose. Projects should either remove all
 *      \c BUTTLOADTAG() elements, or download and extract \c ButtLoadTag.h header from the ButtLoad project.
 *    - The \c Drivers/AT90USBXXX/ directory has been renamed to \c Drivers/Peripheral/.
 *    - The \c Serial_Stream driver has been renamed to \c SerialStream to remain consistent with the rest of the library naming scheme.
 *    - The HWB driver has changed to the \c Buttons driver. See the board Buttons driver documentation for the new API.
 *
 *  <b>Dual Role Mode</b>
 *    - The \c USB_PowerOnFail event has been renamed to \c USB_InitFailure.
 *    - The functions in \c OTG.h have been renamed to remain more consistent with the library API. See the functions in \c OTG.h for more
 *      details.
 *
 *  <b>Device Mode</b>
 *    - The \c Endpoint_ClearCurrentBank() macro has been removed, and is now replaced with the \ref Endpoint_ClearIN(), \ref Endpoint_ClearOUT()
 *      macros. See \c Endpoint.h documentation for more details on the new endpoint management macros.
 *    - The \c Endpoint_ReadWriteAllowed() macro has been renamed to \ref Endpoint_IsReadWriteAllowed() to be more consistent with the rest of
 *      the API naming scheme.
 *    - The \c Endpoint_IsSetupINReady() and \c Endpoint_IsSetupOUTReceived() macros have been renamed to \ref Endpoint_IsINReady() and
 *      \ref Endpoint_IsOUTReceived() respectively.
 *    - The \c Endpoint_IsSetupReceived() macro has been renamed to \ref Endpoint_IsSETUPReceived().
 *    - The \c Endpoint_ClearSetupReceived() macro has been renamed to \ref Endpoint_ClearSETUP().
 *    - All endpoint read/write/discard aliases which did not have an explicitly endianness specifier (such as \c Endpoint_Read_Word()) have
 *      been removed for clarity. Existing projects should use the \c _LE suffix on such calls to use the explicit Little Endian versions.
 *    - The \c USB_UnhandledControlPacket event no longer has any parameters. User code should no longer attempt to read in the remainder of
 *      the Control Request header as all Control Request header data is now preloaded by the library and made available in the
 *      USB_ControlRequest structure.
 *    - The \c FEATURELESS_CONTROL_ONLY_DEVICE token has been renamed to \c CONTROL_ONLY_DEVICE.
 *    - The \c STATIC_ENDPOINT_CONFIGURATION is no longer applicable as the library will apply this optimization when appropriate automatically.
 *    - The values of the \ref Endpoint_Stream_RW_ErrorCodes_t and \ref Endpoint_ControlStream_RW_ErrorCodes_t enums have had the \c ERROR_ portion
 *      of their names removed.
 *
 *  <b>Host Mode</b>
 *    - The \ref USB_Host_SendControlRequest() function no longer automatically selects the Control pipe (pipe 0) to allow it to be used on
 *      other control type pipes. Care should be taken to ensure that the Control pipe is always selected before the function is called
 *      in existing projects where the Control pipe is to be operated on.
 *    - The USB Host management task now saves and restores the currently selected pipe before and after the task runs. Projects no longer
 *      need to manage this manually when calling the USB management task.
 *    - The \c Pipe_ClearCurrentBank() macro has been removed, and is now replaced with the Pipe_ClearIN(), Pipe_ClearOUT() macros. See
 *      Pipe.h documentation for more details on the new pipe management macros.
 *    - The \c Pipe_ReadWriteAllowed() macro has been renamed to \ref Pipe_IsReadWriteAllowed() to be more consistent with the rest of the API
 *      naming scheme.
 *    - The \c Pipe_IsSetupINReceived() and \c Pipe_IsOutReady() macros have been renamed to \ref Pipe_IsINReceived() and \ref Pipe_IsOUTReady()
 *      respectively.
 *    - The new \ref Pipe_ClearSETUP() macro should be used to send SETUP transactions, rather than the previous \c Pipe_ClearSetupOUT() macro.
 *    - The \c Pipe_IsSetupSent() macro has been renamed to \ref Pipe_IsSETUPSent().
 *    - The \c Pipe_ClearSetupSent() macro is no longer applicable and should be removed.
 *    - All pipe read/write/discard aliases which did not have an explicitly endianness specifier (such as \c Pipe_Read_Word()) have
 *      been removed for clarity. Existing projects should use the \c _LE suffix on such calls to use the explicit Little Endian versions.
 *    - The \c Host_IsResetBusDone() macro has been renamed to \c Host_IsBusResetComplete().
 *    - The \c Pipe_Ignore_Word() and \c Pipe_Ignore_DWord() functions have been renamed to \c Pipe_Discard_Word() and \c Pipe_Discard_DWord()
 *      to remain consistent with the rest of the pipe API.
 *    - It is no longer needed to manually include the headers from \c LUFA/Drivers/USB/Class, as they are now included along with the rest
 *      of the USB headers when \c LUFA/Drivers/USB/USB.h is included.
 *    - Functions in the \c ConfigDescriptor.h header file no longer have \c Host_ as part of their names.
 *    - The \c ProcessHIDReport() has been renamed to \ref USB_ProcessHIDReport(), \c GetReportItemInfo() has been renamed to \ref USB_GetHIDReportItemInfo()
 *      and \c SetReportItemInfo() has been renamed to \ref USB_GetHIDReportItemInfo().
 *    - The values of the \ref DSearch_Return_ErrorCodes_t and \ref DSearch_Comp_Return_ErrorCodes_t enums have had their respective \c Descriptor_Search
 *      and \c Descriptor_Search_Comp prefixes changed to all caps.
 *    - The \c USB_HostRequest global has been renamed to \ref USB_ControlRequest, and is used in Device mode also. The \c USB_Host_Request_Header_t
 *      structure type has been renamed to \ref USB_Request_Header_t.
 *    - The values of the \ref Pipe_Stream_RW_ErrorCodes_t enum have had the \c ERROR_ portion of their names removed.
 *
 *  \section Sec_Migration090401 Migrating from 090209 to 090401
 *
 *  <b>All</b>
 *    - LUFA projects must now give the raw input clock frequency (before any prescaling) as a compile time constant \c F_USB,
 *      defined in the project makefile and passed to the compiler via the -D switch.
 *    - The makefile EEPROM programming targets for FLIP and dfu-programmer no longer program in the FLASH data in addition to the
 *      EEPROM data into the device. If both are to be programmed, both the EEPROM and FLASH programming targets must be called.
 *    - As the avr-libc macro has been corrected in recent avr-libc distributions, the \c SetSystemClockPrescaler() macro has been removed.
 *      Include \c <avr/power.h> and call \c clock_prescale_set(clock_div_1); instead on recent avr-libc distributions.
 *
 *  <b>Library Demos</b>
 *    - The USBtoSerial demo now discards all data when not connected to a host, rather than buffering it for later transmission.
 *
 *  <b>Non-USB Library Components</b>
 *    - The \c ATTR_ALWAYSINLINE function attribute macro has been renamed to \ref ATTR_ALWAYS_INLINE.
 *    - Custom board Dataflash drivers now require the implementation of \ref Dataflash_SelectChipFromPage() and \ref Dataflash_SendAddressBytes().
 *
 *  <b>Device Mode</b>
 *    - The \c NO_CLEARSET_FEATURE_REQUEST compile time token has been renamed to \c FEATURELESS_CONTROL_ONLY_DEVICE, and its function expanded
 *      to also remove parts of the Get Status chapter 9 request to further reduce code usage. On all applications currently using the
 *      \c NO_CLEARSET_FEATURE_REQUEST compile time token, it can be replaced with the \c FEATURELESS_CONTROL_ONLY_DEVICE token with no further
 *      modifications required.
 *
 *  \section Sec_Migration090209 Migrating from 081217 to 090209
 *
 *  <b>Device Mode</b>
 *    - The \c ENDPOINT_MAX_ENDPOINTS constant has been renamed to the more appropriate name of \c ENDPOINT_TOTAL_ENDPOINTS.
 *    - The \c USB_STREAM_TIMEOUT_MS stream timeout default period has been extended to 100ms. This can be overridden in the user
 *      makefile if desired to restore the previous 50ms timeout.
 *
 *  <b>Host Mode</b>
 *    - The \c PIPE_MAX_ENDPOINTS constant has been renamed to the more appropriate name of \c PIPE_TOTAL_ENDPOINTS.
 *    - The \c USB_STREAM_TIMEOUT_MS stream timeout default period has been extended to 100ms. This can be overridden in the user
 *      makefile if desired to restore the previous 50ms timeout.
 *    - The \c USB_DeviceEnumerationFailed event now contains a second \c SubErrorCode parameter, giving the error code of the function
 *      which failed.
 *    - The \c HID_PARSE_Sucessful enum member constant name has been corrected to \ref HID_PARSE_Successful.
 *
 *  <b>Non-USB Library Components</b>
 *    - The previous \c SPI_SendByte() functionality is now located in \ref SPI_TransferByte(). \ref SPI_SendByte() now discards the return byte
 *      for speed, to compliment the new \ref SPI_ReceiveByte() function. If bidirectional SPI transfers are required, calls to \ref SPI_SendByte()
 *      should be changed to \ref SPI_TransferByte().
 *    - The serial driver now sets the Tx line as an output explicitly, and enables the pull-up of the Rx line.
 *    - The \ref Serial_Init() and \c SerialStream_Init() functions now take a second \c DoubleSpeed parameter, which indicates if the USART
 *      should be initialized in double speed mode - useful in some circumstances for attaining baud rates not usually possible at the given AVR
 *      clock speed.
 *
 *  \section Sec_Migration171208 Migrating from V1.5.3 to 081217
 *
 *  <b>All</b>
 *    - The MyUSB project name has been changed to LUFA (Lightweight Framework for USB AVRs). All references to MyUSB, including macro names,
 *      have been changed to LUFA.
 *
 *  <b>Library Demos</b>
 *    - The ReconfigureUSART() routine in the USBtoSerial demo was not being called after new line encoding
 *      parameters were set by the host. Projects built on the USBtoSerial code should update to the latest version.
 *    - The HID Parser now supports multiple report (on a single endpoint) HID devices. The MouseHostWithParser and
 *      KeyboardHostWithPaser demos use the updated API functions to function correctly on such devices. Projects
 *      built on either "WithParser" demo should update to the latest code.
 *    - The RNDIS demo TCP stack has been modified so that connections can be properly closed. It is still not
 *      recommended that the MyUSB RNDIS demo TCP/IP stack be used for anything other than demonstration purposes,
 *      as it is neither a full nor a standards compliant implementation.
 *
 *  <b>Non-USB Library Components</b>
 *    - The Serial_IsCharReceived() macro has been changed to the correct spelling of Serial_IsCharReceived() in Serial.h.
 *
 *  <b>Device Mode</b>
 *    - The MANUAL_PLL_CONTROL compile time token has been removed, and replaced with a USB_OPT_MANUAL_PLL mask
 *      to be used in the Options parameter of the USB_Init() function.
 *    - Calling USB_Init() now forces a complete USB interface reset and enumeration, even if the USB interface is
 *      currently initialized.
 *    - Interrupts are now disabled when processing control requests, to avoid problems with interrupts causing the library
 *      or user request processing code to exceed the strict USB timing requirements on control transfers.
 *    - The USB Reset event now resets and disables all device endpoints. If user code depends on endpoints remaining configured
 *      after a Reset event, it should be altered to explicitly re-initialize all user endpoints.
 *    - The prototype for the GetDescriptor function has been changed, as the return value was redundant. The function now
 *      returns the size of the descriptor, rather than passing it back via a parameter, or returns NO_DESCRIPTOR if the specified
 *      descriptor does not exist.
 *    - The NO_DESCRIPTOR_STRING macro has been renamed NO_DESCRIPTOR, and is now also used as a possible return value for the
 *      GetDescriptor function.
 *
 *  <b>Host Mode</b>
 *    - The MANUAL_PLL_CONTROL compile time token has been removed, and replaced with a USB_OPT_MANUAL_PLL mask
 *      to be used in the Options parameter of the USB_Init() function.
 *    - The HID report parser now supports multiple Report IDs. The HID report parser GetReportItemInfo() and
 *      SetReportItemInfo() routines now return a boolean, set if the requested report item was located in the
 *      current report. If sending a report to a multi-report device, the first byte of the report is automatically
 *      set to the report ID of the given report item.
 *    - Calling USB_Init() now forces a complete USB interface reset and enumeration, even if the USB interface is
 *      currently initialized.
 *
 *  \section Sec_Migration152 Migrating from V1.5.2 to V1.5.3
 *
 *  <b>Library Demos</b>
 *    - Previously, all demos contained a serial number string descriptor, filled with all zeros. A serial number
 *      string is required in Mass Storage devices, or devices which are to retain settings when moved between
 *      ports on a machine. As people were not changing the serial number value, this was causing conflicts and so
 *      the serial number descriptor has been removed from all but the Mass Storage demo, which requires it.
 *    - The AudioOut and AudioIn demos did not previously silence their endpoints when the host has deactivated
 *      them. Projects built upon either demo should upgrade to the latest code.
 *    - The FEATURE_ENDPOINT macro has been renamed FEATURE_ENDPOINT_HALT, and is now correctly documented.
 *    - The MassStoreHost demo contained errors which caused it to lock up randomly on certain devices. Projects built
 *      on the MassStoreDemo code should update to the latest version.
 *    - The Interrupt type endpoint in the CDC based demos previously had a polling interval of 0x02, which caused
 *      problems on some Linux systems. This has been changed to 0xFF, projects built on the CDC demos should upgrade
 *      to the latest code.
 *    - The HID keyboard and mouse demos were not previously boot mode compatible. To enable boot mode support, projects
 *      built on the keyboard or mouse demos (or derivatives) should upgrade to the latest code.
 *    - The Mass Storage demo was not previously standards compliant. Projects built on the Mass Storage demo should
 *      upgrade to the latest code.
 *    - The USART was not being reconfigured after the host sent new encoding settings in the USBtoSerial demo. This was
 *      previously discovered and fixed, but the change was lost. Projects built on the USBtoSerial demo should update
 *      to the latest code.
 *
 *  <b>Device Mode</b>
 *    - The endpoint non-control stream functions now have a default timeout of 50ms between packets in the stream.
 *      If this timeout is exceeded, the function returns the new ENDPOINT_RWSTREAM_ERROR_Timeout error value. The
 *      timeout value can be overridden by defining the USB_STREAM_TIMEOUT_MS in the project makefile to the desired
 *      timeout duration in ms.
 *    - Rather than returning fixed values, the flags indicating if the device has Remote Wakeup currently enabled
 *      and/or is self-powered are now accessed and set through the new USB_RemoteWakeupEnabled and
 *      USB_CurrentlySelfPowered macros. See the DevChapter9.h documentation for more details.
 *    - All endpoint stream functions now require an extra Callback function parameter. Existing code may be updated
 *      to either supply NO_STREAM_CALLBACK as the extra parameter, or disable stream callbacks altogether by passing
 *      the token NO_STREAM_CALLBACKS to the compiler using the -D switch.
 *
 *  <b>Host Mode</b>
 *    - The pipe non-control stream functions now have a default timeout of 50ms between packets in the stream.
 *      If this timeout is exceeded, the function returns the new PIPE_RWSTREAM_ERROR_Timeout error value. The
 *      timeout value can be overridden by defining the USB_STREAM_TIMEOUT_MS in the project makefile to the desired
 *      timeout duration in ms.
 *    - CollectionPath_t has been renamed to HID_CollectionPath_t to be more in line with the other HID parser structures.
 *    - All pipe stream functions now require an extra Callback function parameter. Existing code may be updated
 *      to either supply NO_STREAM_CALLBACK as the extra parameter, or disable stream callbacks altogether by passing
 *      the token NO_STREAM_CALLBACKS to the compiler using the -D switch.
 *
 *  \section Sec_Migration151 Migrating from V1.5.1 to V1.5.2
 *
 *  <b>Library Demos</b>
 *    - The RNDIS demo application has been updated so that it is functional on Linux under earlier implementations
 *      of the RNDIS specification, which had non-standard behaviour. Projects built upon the demo should upgrade
 *      to the latest code.
 *    - The DFU class bootloader has had several bugs corrected in this release. It is recommended that where
 *      possible any existing devices upgrade to the latest bootloader code.
 *
 *  \section Sec_Migration150 Migrating from V1.5.0 to V1.5.1
 *
 *  <b>Library Demos</b>
 *    - The USBtoSerial demo was broken in the 1.5.0 release, due to incorrect register polling in place of the
 *      global "Transmitting" flag. The change has been reverted in this release. Projects built upon the demo
 *      should upgrade to the latest code.
 *    - The HID class demos did not implement the mandatory GetReport HID class request. Projects built upon the HID
 *      demos should upgrade to the latest code.
 *    - The HID class demos incorrectly reported themselves as boot-protocol enabled HID devices in their descriptors.
 *      Projects built upon the HID demos should upgrade to the latest code.
 *    - The MIDI device demo had incorrect AudioStreaming interface descriptors. Projects built upon the MIDI demo
 *      should upgrade to the latest code.
 *    - The AudioOut demo did not correctly tristate the speaker pins when USB was disconnected, wasting power.
 *      Projects built upon the AudioOut demo should upgrade to the latest code.
 *
 *  \section Sec_Migration141 Migrating from V1.4.1 to V1.5.0
 *
 *  <b>Library Demos</b>
 *    - Previous versions of the library demos had incorrectly encoded BCD version numbers in the descriptors. To
 *      avoid such mistakes in the future, the VERSION_BCD macro has been added to StdDescriptors.h. Existing
 *      projects should at least manually correct the BCD version numbers, or preferably update the descriptors to
 *      encode the version number in BCD format using the new macro.
 *    - The mandatory GetReport class-specific request was accidentally omitted from previous versions of the demos
 *      based on the Human Interface Device (HID) class. This has been corrected, and any user projects based on the
 *      HID demos should also be updated accordingly.
 *    - The CDC demos now correctly send an empty packet directly after a full packet, to end the transmission.
 *      Failure to do this on projects which always or frequently send full packets will cause buffering issues on
 *      the host OS. All CDC user projects are advised to update their transmission routines in the same manner as
 *      the library CDC demos.
 *    - The previous interrupt-driven Endpoint/Pipe demos did not properly save and restore the currently selected
 *      Endpoint/Pipe when the ISR fired. This has been corrected - user projects based on the interrupt driven
 *      demos should also update to properly save and restore the selected Endpoint/Pipe.
 *
 *  <b>Non-USB Library Components</b>
 *    - The Atomic.h and ISRMacro.h header files in MyUSB/Common have been removed, as the library is now only
 *      compatible with avr-libc library versions newer than the time before the functionality of the deleted
 *      headers was available.
 *
 *  <b>Device Mode</b>
 *    - The GetDescriptor function (see StdDescriptors.h) now has a new prototype, with altered parameter names and
 *      functions. Existing projects will need to update the GetDescriptor implementation to reflect the new API.
 *      The previously split Type and Index parameters are now passed as the original wValue parameter to the
 *      function, to make way for the USB specification wIndex parameter which is <i>not</i> the same as the
 *      previous Index parameter.
 *    - The USB_UnhandledControlPacket event (see Events.h) now has new parameter names, to be in line with the
 *      official USB specification. Existing code will need to be altered to use the new parameter names.
 *    - The USB_CreateEndpoints event (see Events.h) has been renamed to USB_ConfigurationChanged, which is more
 *      appropriate. It fires in an identical manner to the previously named event, thus the only change to be made
 *      is the event name itself in the user project.
 *    - The USB_Descriptor_Language_t structure no longer exists in StdDescriptors.h, as this was a
 *      pseudo-descriptor modeled on the string descriptor. It is replaced by the true USB_Descriptor_String_t type
 *      descriptor as indicated in the USB specification, thus all device code must be updated accordingly.
 *    - The names of several Endpoint macros have been changed to be more consistent with the rest of the library,
 *      with no implementation changes. This means that existing code can be altered to use the new macro names
 *      with no other considerations required. See Endpoint.h for the new macro names.
 *    - The previous version of the MassStorage demo had an incorrect value in the SCSI_Request_Sense_Response_t
 *      structure named SenseData in SCSI.c which caused some problems with some hosts. User projects based on this
 *      demo should correct the structure value to maintain compatibility across multiple OS platforms.
 *    - By default, the descriptor structures use the official USB specification names for the elements. Previous
 *      versions of the library used non-standard (but more verbose) names, which are still usable in the current
 *      and future releases when the correct compile time option is enabled. See the StdDescriptors.h file
 *      documentation for more details.
 *
 *  <b>Host Mode</b>
 *    - The USB_Host_Request_Header_t structure in HostChapter9.h (used for issuing control requests) has had its
 *      members renamed to the official USB specification names for requests. Existing code will need to be updated
 *      to use the new names.
 *    - The names of several Pipe macros have been changed to be more consistent with the rest of the library,
 *      with no implementation changes. This means that existing code can be altered to use the new macro names
 *      with no other considerations required. See Pipe.h for the new macro names.
 *    - By default, the descriptor structures use the official USB specification names for the elements. Previous
 *      versions of the library used non-standard (but more verbose) names, which are still usable in the current
 *      and future releases when the correct compile time option is enabled. See the StdDescriptors.h file
 *      documentation for more details.
 *    - The names of the macros in Host.h for controlling the SOF generation have been renamed, see the Host.h
 *      module documentation for the new macro names.
 *
 *  <b>Dual Role Mode</b>
 *    - The OTG.h header file has been corrected so that the macros now perform their stated functions. Any existing
 *      projects using custom headers to fix the broken OTG header should now be altered to once again use the OTG
 *      header inside the library.
 *    - The USB_DeviceEnumerationComplete event (see Events.h) now also fires in Device mode, when the host has
 *      finished enumerating the device. Projects relying on the event only firing in Host mode should be updated
 *      so that the event action only occurs when the USB_Mode global is set to USB_MODE_HOST.
 */