I may be asking about something that has already been done, so apologies if that is the case...
I have a USB GPS plugged into one of the USB ports on my RPi(2). It works now in that GPS data is passed and processed by RPi based applications.
What I want to do, is to take that same GPS data string moving to/from the GPS device via the RPi's USB port and move it to/from the GPIO as TTL level (not RS-232, but serial nonetheless) data that it may be used on other devices which do not have USB host capability and therefor cannot communicate to a USB GPS.
In the current setup, most application are looking at the USB GPS as being on a virtual com port (/dev/ttyUSBxx).
So I suppose what I am wanting to do is send/receive serial GPS data between a USB based virtual com port and a GPIO virtual com port.
A virtual 'router' or 'message switch' if you will.
What I am NOT looking to create is a USB port using the GPIO.
Physical: USB GPS <---> RPi USB port---RPi GPIO <---> GPS Data to/from other devices.
Logical: USB GPS Data <----- GPS Data Routed in RPi ----> GPIO GPS Data