Add an indirection between the common serial communication code and the
libserialport specific support code. Prepare the use of alternative
transports like USB HID in the future. Decide in the open() routine
which transport to use for subsequent operations (based on port names).
In theory only the transport specific layer depends on the libserialport
library's availability. In this implementation all support for serial
communication still depends on the HAVE_LIBSERIALPORT preprocessor
symbol. This needs to get addressed in later commits.
Add a serial_has_receive_data() routine to the serial layer's API which
returns the number of (known to be) available RX data bytes. Implement
support in the libserialport specific code.
Introduce a new serial_libsp.c source file, and move code from serial.c
there which is specific to libserialport. Keep the existing serial.c API
in place, this is a pure internal refactoring.
Adjust a little whitespace while we are here. Rearrange long lines to
keep related parameter groups adjacent (like pointer and size, or UART
frame length and flow control). Consistently reduce indentation of
continuation lines.
Uwe Hermann
Gerhard Sittig