Use uos.dupterm for REPL configuration of the main USB_VCP(0) stream on
dupterm slot 1, if USB is enabled. This means dupterm can also be used to
disable the boot REPL port if desired, via uos.dupterm(None, 1).
For efficiency this adds a simple hook to the global uos.dupterm code to
work with streams that are known to be native streams.
With this and previous patches the stm32 port can now be compiled using
object representation D (nan boxing). Note that native code and frozen mpy
files with float constants are currently not supported with this object
representation.
This patch adds the configuration MICROPY_HW_USB_ENABLE_CDC2 which enables
a new USB device configuration at runtime: VCP+VCP+MSC. It will give two
independent VCP interfaces available via pyb.USB_VCP(0) and pyb.USB_VCP(1).
The first one is the usual one and has the REPL on it. The second one is
available for general use.
This configuration is disabled by default because if the mode is not used
then it takes up about 2200 bytes of RAM. Also, F4 MCUs can't support this
mode on their USB FS peripheral (eg PYBv1.x) because they don't have enough
endpoints. The USB HS peripheral of an F4 supports it, as well as both the
USB FS and USB HS peripherals of F7 MCUs.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
