Raspberry Pi使用USB一起交谈

Question

I want to develop a PyUSB program which listens to data from USB. However, I wish to expand the application to talk another Raspberry Pi through USB port. I wonder is it possible?

Answer 1

USB is a master/slave protocol where a USB device is connected to a USB host . You cannot directly connect a USB host to a USB host. The RPi is a USB host.

What is possible however is to use two USB devices that connect via some other interface such as UART and each connect to a different host. For example you could use two FTDI USB/Serial bridge devices back-to-back:

                    __________      ________
                    |     Tx |______|Rx     |
USB Host A ---------|     Rx |______|Tx     |---------USB Host B
                    |________|      |_______|
                      FT323R         FT323R

As such it is largely a hardware problem not a software problem. The data rate will be limited by the capability of the USB/Serial device - 3MBaud for the FT232. Note that a real implementation you would also connect the RTS/CTS flow control pins, but there is a limit to my ASCII diagramming patience!

A probably better solution is to use a commercially available USB bridge cable ; these use the same principle as serial bridge solution described above, but instead of emulating a COM/TTY port, emulate an network interface and can run at full USB speed. You could of course implement such a cable but I doubt it would be cost effective even compared with solution I suggested above. I do not know whether suitable drivers for USB network adapters exist for RPi however.

Given that RPi has Ethernet, that would be a far simpler method of board to board communication and is not limited to point-to-point, but can access an entire network, and there will be no USB driver issues to tackle.