Apparantly, the windows wingdi.h header file already defines the
ERROR macro. By defining the NOGDI macro before including the
windows.h header file, we can prevent the wingdi.h file from being
included and thus avoid the warning. We don't need that header for
anything anyway.
Because the libusb header file includes the windows.h file
explicitly, it needs the same fix.
The public header files are moved to a new subdirectory, to separate
the definition of the public interface from the actual implementation.
Using an identical directory layout as the final installation has the
advantage that the example code can be build outside the project tree
without any modifications to the #include statements.
When using half-duplex communication (e.g. only a single wire for both
Tx and Rx) a data packet needs to be transmitted entirely before
attempting to switch into receiving mode.
For legacy serial hardware, the tcdrain() probably works as advertised,
and waits until the data has been transmitted. However for common
usb-serial converters, the hardware doesn't provide any feedback to the
driver, and the tcdrain() function can only wait until the data has been
transmitted to the usb-serial chip. There is no guarantee that the data
has actually been transmitted by the usb-serial chip.
As a workaround, we wait at least the minimum amount of time required to
transmit the data packet over a serial line, taking into account the
current configuration.
The "\\.\" prefix allows to access the Win32 device namespace directly,
without going through the file system. This is required to support
non-standard port names, and COMx ports with a number greater than 9.
