The main purpose of this new COM implementation is that it is
much simpler, and requires less code space. This takes a bit
of the pressure off of the CC bootloader which was right at
the limit of available code space in the bootloader partition.
This is not intended to ever be used by the application.
This driver also formalizes the assumptions in the bootloader's
usage of the COM layer. All messages are assumed to arrive
in atomic chunks from the HID layer.
Summary of changes:
* USB CDC and HID drivers are completely split apart.
* This will allow different max buffer sizes for HID and CDC.
* USB descriptors have been overhauled:
* Proper structs/macros/enums declared for USB (see pios_usb_defs.h)
* Two common descriptor definitions. One for HID+CDC another for HID only.
See pios_usb_desc_{hid_cdc,hid_only}.c for details.
* Long standing bugs in OP USB descriptors became much more obvious with the
new struct definitions.
* Board specific USB initialization is now in pios_usb_board_data.h in each build target.
* Definition of USB descriptors is now entirely indpendent of STM32 libs.
Glue into STM32 libs is provided by pios_usbhook.c.
* Removed a lot of stale/irrelevant USB #defines throughout the tree.
* Improved naming consistency throughout USB code:
* PIOS_USB_HID_* now refers to the HID endpoint code.
* PIOS_USB_CDC_* now refers to the CDC endpoint code.
* PIOS_USB_* now refers to the low-level USB code.
* PIOS_USB_BOARD_* now refers to board-specific USB data
* PIOS_USBHOOK_* is glue between PIOS and STM32 USB libs.
* struct usb_* and enum usb_* and USB_* and HID_* are all types from the USB spec.
* Shrunk the buffer size on the CDC call mgmt endpoint to save some RAM.
* Made a few more USB related variables static to save some RAM.
