I'm a new user to Raspberry Pi and this is my first Pi project. I'm running the latest version of Raspbian.


How do I configure my Raspberry Pi 3 B+ to map one USB port to another? One port has a thumb-drive and the other would be connected to my vehicle radio.


I have a radio receiver in my pickup truck that can play mp3, mp4 content stored on a USB thumb drive when plugged into the radio. When I want to change the content it always takes me several days to remember to bring the thumb-drive in, several more to change the content, then several more to remember to take it back out. I thought putting Pi in between the radio and thumb-drive would be a cool hack.

What I've done so far:

I've permanently mounted a thumb-drive to the Pi. When I pull into the driveway, the Pi automatically connects to my home WiFi and shows up on my PC as a mapped drive.

  • I can manually drag and drop content to it or..
  • My NAS automatically backs up from a share to the USB drive on the Pi. I can sit at my computer in the evening, drop content into the share and overnight the NAS synchs the Share's content with what's on the Pi's thumb-drive.
  • Transfer rate is 8-10 MB/sec which is plenty fast enough for me.


  • 1
    you are asking the wrong question ..... you do not want to map any USB ports ..... all you want to do is to use an RPi to emulate a thumb drive
    – jsotola
    Dec 30, 2018 at 22:23
  • As @goldilocks points out this is not possible with Raspberry Pi B models - because their USB connections are all USB-A type sockets which are connected to a USB hub which has to be the up-stream connection. However the Zero models only have a single micro USB A connection which has the feature that it is wired directly to the SoC at the heart of an RPi and can be switched to the On-The-Go mode.
    – SlySven
    Dec 31, 2018 at 13:50

1 Answer 1


You can't.

Devices which have USB passthrough are slave devices -- keyboards, cases, etc. The Pi 3 cannot be used as a slave device. I'll repeat myself from here:

USB is not a symmetrical protocol, meaning the two parties in a relationship are not equals. One is the master, and one is the slave. This is controlled in hardware, and although I believe it would be pretty simple to make a standard USB A port serve either role, conventionally they do not, I presume to prevent accidents, since plugging a master into a master can cause physical damage to one or both machines -- which is why you should never plug an A port into another A port (male-to-male cables for which are in fact hard to find).

If your car stereo has a standard USB A jack that you can plug a thumb drive into, that port is a master. So are the ones on the Pi 3, end-of-story.

As per the quote, this is the exact same reason you cannot connect your laptop to your desktop using a USB cable for data exchange.

You could use a Pi Zero, which has OTG functionality (see the link above), to emulate a thumb drive, as jsotola suggests.

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