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.

Migrating from 111009 to 120219

USB Core

The HID_KEYBOARD_MODIFER_* macros in the HID class driver have been corrected to HID_KEYBOARD_MODIFIER_* (note the spelling of "modifier"). Existing applications should switch over to the correctly spelled macro names.
The names of the USB Device and USB Host class driver files have changed; a new "ClassDevice" and "ClassHost" postfix has been added to the respective class driver files. Projects referencing the class driver source files by filename rather than the LUFA_SRC_USBCLASS makefile variable should append these postfixes to the source file names. Projects including the USB class driver dispatch headers directly should either switch to including the main USB driver header instead, or use the updated header filenames.
The USB_CONFIG_ATTR_BUSPOWERED constant has been renamed to USB_CONFIG_ATTR_RESERVED, as this was misnamed. All devices must set this bit in the Configuration descriptor's attributes field. As all devices are assumed to be bus-powered unless stated otherwise with the USB_CONFIG_ATTR_SELFPOWERED flag a replacement constant for bus powered devices is not provided.

Device Mode

The device mode Audio class driver now requires a new user application callback, CALLBACK_Audio_Device_GetSetInterfaceProperty(). Existing applications must implement this new callback, however if no audio entities are defined in the audio device's descriptors, this function may be hard-coded to always return false for previous behaviour to be retained.

Migrating from 110528 to 111009

Non-USB Library Components

The JTAG_DEBUG_ASSERT() macro has been renamed JTAG_ASSERT() to be consistent with STDOUT_ASSERT().

USB Core

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 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 F_CLOCK symbol, required in the project makefile, has been renamed to 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.

Device Mode

The Endpoint stream functions now all require a BytesProcessed parameter instead of the previous callback parameter. This should be set to 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 NULL, each time the endpoint bank becomes full and the packet is sent, the routine will exit with the new ENDPOINT_RWSTREAM_IncompleteTransfer error code to allow the user application to determine when to send the next chunk of data.
The CDC_Device_SendString() function now expects a null terminated string instead of an explicit length. Existing code should use the new CDC_Device_SendData() function, or remove the length parameter from the function call.
The Endpoint_ResetFIFO() function has been renamed to 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 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 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 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 RNDIS_Device_ReadPacket() and/or RNDIS_Device_SendPacket().
The definition of the Audio class USB_Audio_Descriptor_Format_t has been altered, to remove the fixed singular audio sample rate in the descriptor definition, and to rename the SampleFrequencyType to the more appropriate TotalDiscreteSampleRates. Existing applications will need to add an array of USB_Audio_SampleFreq_t elements immediately following any 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, 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 USB_ConfigurationNumber, USB_RemoteWakeupEnabled and USB_CurrentlySelfPowered globals have been renamed to USB_Device_ConfigurationNumber, USB_Device_RemoteWakeupEnabled and 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 ENDPOINT_DESCRIPTOR_DIR_IN and ENDPOINT_DESCRIPTOR_DIR_OUT macros have now been replaced by ENDPOINT_DIR_IN and ENDPOINT_DIR_OUT to improve code clarity.
The HID_DESCRIPTOR_JOYSTICK() macro now takes an additional (first) parameter indicating the number of axis in the joystick.

Host Mode

The Pipe stream functions now all require a BytesProcessed parameter instead of the previous callback parameter. This should be set to 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 NULL, each time the pipe bank becomes full and the packet is sent, the routine will exit with the new PIPE_RWSTREAM_IncompleteTransfer error code to allow the user application to determine when to send the next chunk of data.
The PRNT_Host_SendString() and CDC_Host_SendString() functions now expect a null terminated string instead of an explicit length. Existing code should use the new PRNT_Host_SendData() and CDC_Host_SendData() functions, or remove the length parameter from the function call.
The Pipe_ClearErrorFlags() function has been removed, as the pipe error flags are now automatically cleared when the Pipe_ClearError() function is called.
The 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 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 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 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.

Migrating from 100807 to 101122

USB Core

A new USB driver source file, 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, 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 EVENT_USB_InitFailure() event has been removed, as the 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 USB_Modes_t enum.
All class driver headers are now included as part of the standard 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.

Device Mode

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 CALLBACK_USB_GetDescriptor() callback has changed, the void** const DescriptorAddress parameter is now const void** const DescriptorAddress. Existing applications should update their callback signatures to match this, and eliminate any casting of descriptor pointers to a non 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 ENDPOINT_DOUBLEBANK_SUPPORTED() macro is has been renamed 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 EVENT_USB_Device_UnhandledControlRequest() event is now named 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.

Host Mode

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 PRNT_Host_SendData() function has been renamed to 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 SImage_ to SI_, to remain consistent with the rest of the driver's enums, type defines and constants.

Migrating from 100513 to 100807

Non-USB Library Components

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.

USB Core

A new USB driver source file, 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 Drivers/USB/LowLevel/DevChapter9.c source file has moved to 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 Drivers/USB/LowLevel/HostChapter9.h source file has moved to 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 Drivers/USB/LowLevel/LowLevel.c source file has moved to 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.

Device Mode

The USB_Device_IsRemoteWakeupSent() macro has been removed, as the remote wakeup request is now fully handled by the enhanced USB_Device_SendRemoteWakeup() function. Existing code may now discard any checks to USB_Device_IsRemoteWakeupSent().
The USB_Device_IsUSBSuspended() macro has been removed, as it is obsolete. Existing code should compare USB_DeviceState to see if it the device is in the DEVICE_STATE_Suspended state instead.
The 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 CDC_Device_BytesReceived() is no longer needed if the exact number of queued bytes received is not needed.

Host Mode

The 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 CDC_Host_BytesReceived() is no longer needed if the exact number of queued bytes received is not needed.
The CDC_Host_USBTask() now calls 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 CDC_Host_USBTask().

Migrating from 100219 to 100513

Non-USB Library Components

The TWI_StartTransmission() function now takes in a timeout period, expressed in milliseconds, within which the addressed device must respond or the function will abort.

Device Mode

The USB_Init() function no longer calls 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 USB_Init() to ensure that the enumeration process functions correctly.
The USBInterrupt.c USB driver source file has been relocated from LUFA/Drivers/USB/HighLevel/ to LUFA/Drivers/USB/LowLevel. Projects must update their makefile SRC values accordingly.
The HID Device Class driver's function signature for the CALLBACK_HID_Device_ProcessHIDReport() function has been changed, to allow for a new 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.

Host Mode

The USB_Init() function no longer calls 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 USB_Init() to ensure that the enumeration process functions correctly.
The USBInterrupt.c USB driver source file has been relocated from LUFA/Drivers/USB/HighLevel/ to LUFA/Drivers/USB/LowLevel. Projects must update their makefile SRC values accordingly.
The HID Host Class driver's function signature for the HID_Host_SendReportByID() function has been changed, to allow for a new ReportType parameter. Existing calls to this function should substitute REPORT_ITEM_TYPE_Out as this parameter's value.

Migrating from 091223 to 100219

Non-USB Library Components

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 ADC Driver - LUFA/Drivers/Peripheral/ADC.h). These masks should be used when calling the ADC functions to ensure proper operation across all AVR models. Note that the ADC_SetupChannel() function is an exception, and should always be called with a channel number rather than a channel mask.

Host Mode

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 MIDI_Host_Flush().
The 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 PIPE_EPNUM_MASK token before calling Pipe_IsEndpointBound().

Device Mode

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 MIDI_Device_Flush().

Migrating from 091122 to 091223

Host Mode

The Still Image Host Class driver SI_Host_USBTask() and SI_Host_ConfigurePipes() functions were misnamed, and are now named SImage_Host_USBTask() and SImage_Host_ConfigurePipes() respectively.
The HOST_SENDCONTROL_DeviceDisconnect enum value has been renamed to 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.

Device Mode

The CALLBACK_HID_Device_CreateHIDReport() HID Device Class driver callback now has a new ReportType parameter to indicate the report type to generate. Existing applications may simply add and ignore this additional parameter.

Migrating from 090924 to 091122

Host Mode

The HID_PARSE_UsageStackOverflow HID parser error constant is now named HID_PARSE_UsageListOverflow
The CALLBACK_HIDParser_FilterHIDReportItem() HID Parser callback now passes a complete HID_ReportItem_t to the user application, instead of just its attributes.
The USB_GetDeviceConfigDescriptor() function was incorrectly named and is now called USB_Host_GetDeviceConfigDescriptor().

Migrating from 090810 to 090924

Non-USB Library Components

The ADC_Off() function has been renamed to ADC_ShutDown() to be consistent with the rest of the library.
The SPI_Init() routine's parameters have changed, so that the clock polarity and data sampling modes can be set. See the SPI_Init() function documentation for more details
The Dataflash_Init() routine no longer initializes the SPI bus - the SPI bus should be initialized manually via a call to SPI_Init() before using the Dataflash driver

Host Mode

The 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 CALLBACK_HIDParser_FilterHIDReportItem().
The HID report parser now always parses FEATURE and always ignores constant-data items - the HID_ENABLE_FEATURE_PROCESSING and HID_INCLUDE_CONSTANT_DATA_ITEMS compile time tokens now have no effect.
The USE_NONSTANDARD_DESCRIPTOR_NAMES compile time token has been removed - there are now separate USB_Descriptor_* and 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 USB_StdDescriptor_* variants.

Device Mode

The USE_NONSTANDARD_DESCRIPTOR_NAMES compile time token has been removed - there are now separate USB_Descriptor_* and 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 USB_StdDescriptor_* variants.

Migrating from 090605 to 090810

All

The "Simple Scheduler" has been deprecated, 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.

Non-USB Library Components

The ATTR_NOINLINE function attribute macro has been renamed to ATTR_NO_INLINE to be in line with the rest of the function attribute macro names.

Library Demos

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.

Host Mode

The HIDParser.c module has moved from LUFA/Drivers/USB/Class/ to LUFA/Drivers/USB/Class/Host/.
The 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 HOST_STATE_Configured code should be moved to the end of the existing HOST_STATE_Addressed state, and the existing HOST_STATE_Ready state code should be moved to the HOST_STATE_Configured state.
The USB_IsConnected global has been removed, as it is too vague for general use. Test 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 USB Events page for details on the new event names and firing conditions.

Device Mode

The 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 USE_FLASH_DESCRIPTORS token in the project makefile to fix all descriptors into FLASH space and remove the extra function parameter.
The USB_IsSuspended global has been removed - test USB_DeviceState against DEVICE_STATE_Suspended instead.
The USB_IsConnected global has been removed, as it is too vague for general use. Test 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 USB_Connect and 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 USB Events page for details on the new event names and firing conditions.

Migrating from 090510 to 090605

Device Mode

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 INTERRUPT_CONTROL_ENDPOINT token defined.
The 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 USB Events for new API details.
The 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 uint8_t value.
The Event_DeviceError() event no longer exists, as its sole caller (unlinked USB_GetDescriptor() function) now produces a compilation error rather than a runtime error. The StdDescriptors.c file no longer exists as a result, and should be removed from project makefiles.
The USB_GetDescriptor() function has been renamed to CALLBACK_USB_GetDescriptor() to be in line with the new CALLBACK_ function prefixes for functions which must be implemented in the user application.

Host Mode

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 USB Events for new API details.
The 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 uint8_t value.
The 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 uint8_t value.

Migrating from 090401 to 090510

All

The ButtLoadTag.h header has been removed, as it was never used for its intended purpose. Projects should either remove all BUTTLOADTAG() elements, or download and extract ButtLoadTag.h header from the ButtLoad project.
The Drivers/AT90USBXXX/ directory has been renamed to Drivers/Peripheral/.
The Serial_Stream driver has been renamed to SerialStream to remain consistent with the rest of the library naming scheme.
The HWB driver has changed to the Buttons driver. See the board Buttons driver documentation for the new API.

Dual Role Mode

The USB_PowerOnFail event has been renamed to USB_InitFailure.
The functions in OTG.h have been renamed to remain more consistent with the library API. See the functions in OTG.h for more details.

Device Mode

The Endpoint_ClearCurrentBank() macro has been removed, and is now replaced with the Endpoint_ClearIN(), Endpoint_ClearOUT() macros. See Endpoint.h documentation for more details on the new endpoint management macros.
The Endpoint_ReadWriteAllowed() macro has been renamed to Endpoint_IsReadWriteAllowed() to be more consistent with the rest of the API naming scheme.
The Endpoint_IsSetupINReady() and Endpoint_IsSetupOUTReceived() macros have been renamed to Endpoint_IsINReady() and Endpoint_IsOUTReceived() respectively.
The Endpoint_IsSetupReceived() macro has been renamed to Endpoint_IsSETUPReceived().
The Endpoint_ClearSetupReceived() macro has been renamed to Endpoint_ClearSETUP().
All endpoint read/write/discard aliases which did not have an explicitly endianness specifier (such as Endpoint_Read_Word()) have been removed for clarity. Existing projects should use the _LE suffix on such calls to use the explicit Little Endian versions.
The 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 FEATURELESS_CONTROL_ONLY_DEVICE token has been renamed to CONTROL_ONLY_DEVICE.
The STATIC_ENDPOINT_CONFIGURATION is no longer applicable as the library will apply this optimization when appropriate automatically.
The values of the Endpoint_Stream_RW_ErrorCodes_t and Endpoint_ControlStream_RW_ErrorCodes_t enums have had the ERROR_ portion of their names removed.

Host Mode

The 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 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 Pipe_ReadWriteAllowed() macro has been renamed to Pipe_IsReadWriteAllowed() to be more consistent with the rest of the API naming scheme.
The Pipe_IsSetupINReceived() and Pipe_IsOutReady() macros have been renamed to Pipe_IsINReceived() and Pipe_IsOUTReady() respectively.
The new Pipe_ClearSETUP() macro should be used to send SETUP transactions, rather than the previous Pipe_ClearSetupOUT() macro.
The Pipe_IsSetupSent() macro has been renamed to Pipe_IsSETUPSent().
The 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 Pipe_Read_Word()) have been removed for clarity. Existing projects should use the _LE suffix on such calls to use the explicit Little Endian versions.
The Host_IsResetBusDone() macro has been renamed to Host_IsBusResetComplete().
The Pipe_Ignore_Word() and Pipe_Ignore_DWord() functions have been renamed to Pipe_Discard_Word() and Pipe_Discard_DWord() to remain consistent with the rest of the pipe API.
It is no longer needed to manually include the headers from LUFA/Drivers/USB/Class, as they are now included along with the rest of the USB headers when LUFA/Drivers/USB/USB.h is included.
Functions in the ConfigDescriptor.h header file no longer have Host_ as part of their names.
The ProcessHIDReport() has been renamed to USB_ProcessHIDReport(), GetReportItemInfo() has been renamed to USB_GetHIDReportItemInfo() and SetReportItemInfo() has been renamed to USB_GetHIDReportItemInfo().
The values of the DSearch_Return_ErrorCodes_t and DSearch_Comp_Return_ErrorCodes_t enums have had their respective Descriptor_Search and Descriptor_Search_Comp prefixes changed to all caps.
The USB_HostRequest global has been renamed to USB_ControlRequest, and is used in Device mode also. The USB_Host_Request_Header_t structure type has been renamed to USB_Request_Header_t.
The values of the Pipe_Stream_RW_ErrorCodes_t enum have had the ERROR_ portion of their names removed.

Migrating from 090209 to 090401

All

LUFA projects must now give the raw input clock frequency (before any prescaling) as a compile time constant 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 SetSystemClockPrescaler() macro has been removed. Include <avr/power.h> and call clock_prescale_set(clock_div_1); instead on recent avr-libc distributions.

Library Demos

The USBtoSerial demo now discards all data when not connected to a host, rather than buffering it for later transmission.

Non-USB Library Components

The ATTR_ALWAYSINLINE function attribute macro has been renamed to ATTR_ALWAYS_INLINE.
Custom board Dataflash drivers now require the implementation of Dataflash_SelectChipFromPage() and Dataflash_SendAddressBytes().

Device Mode

The NO_CLEARSET_FEATURE_REQUEST compile time token has been renamed to 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 NO_CLEARSET_FEATURE_REQUEST compile time token, it can be replaced with the FEATURELESS_CONTROL_ONLY_DEVICE token with no further modifications required.

Migrating from 081217 to 090209

Device Mode

The ENDPOINT_MAX_ENDPOINTS constant has been renamed to the more appropriate name of ENDPOINT_TOTAL_ENDPOINTS.
The 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.

Host Mode

The PIPE_MAX_ENDPOINTS constant has been renamed to the more appropriate name of PIPE_TOTAL_ENDPOINTS.
The 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 USB_DeviceEnumerationFailed event now contains a second SubErrorCode parameter, giving the error code of the function which failed.
The HID_PARSE_Sucessful enum member constant name has been corrected to HID_PARSE_Successful.

Non-USB Library Components

The previous SPI_SendByte() functionality is now located in SPI_TransferByte(). SPI_SendByte() now discards the return byte for speed, to compliment the new SPI_ReceiveByte() function. If bidirectional SPI transfers are required, calls to SPI_SendByte() should be changed to SPI_TransferByte().
The serial driver now sets the Tx line as an output explicitly, and enables the pull-up of the Rx line.
The Serial_Init() and SerialStream_Init() functions now take a second 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.

Migrating from V1.5.3 to 081217

All

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.

Library Demos

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.

Non-USB Library Components

The Serial_IsCharReceived() macro has been changed to the correct spelling of Serial_IsCharReceived() in Serial.h.

Device Mode

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.

Host Mode

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.

Migrating from V1.5.2 to V1.5.3

Library Demos

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.

Device Mode

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.

Host Mode

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.

Migrating from V1.5.1 to V1.5.2

Library Demos

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.

Migrating from V1.5.0 to V1.5.1

Library Demos

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.

Migrating from V1.4.1 to V1.5.0

Library Demos

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.

Non-USB Library Components

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.

Device Mode

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 not 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.

Host Mode

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.

Dual Role Mode

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.