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I am trying to design the following. My Android device (and the applications processor on board) has a limitation of a single USB PHY only. enter image description here

Here is my goal. I have to support the Android box in USB-OTG mode. I have to support simultaneous operation of Keyboard/mouse and also to a PC so that I can do a file transfer to the Android box.

Adding the USB-Hub is the easy part. But I don't think there are existing solutions to hacks that I am aware of doing Android Host to PC Host and emulating Mass storage for file transfer.

Can somebody help? If there are possible solutions.

I have googled around, and found that I can add in a microcontroller bridge in between the Hub and the PC to emulate this. However I am not understanding how this works, i.e. wouldn't the Microcontroller still be a USB downstream??

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  • \$\begingroup\$ Skip the usb keyboard and go with a Bluetooth one. Then you don't have to worry and can connect the PC as a normal host. \$\endgroup\$
    – Passerby
    Feb 26, 2017 at 23:53
  • \$\begingroup\$ Unfortunately my Android device currently doesn't support Bluetooth. So I am kinda stuck with a wired solution only. \$\endgroup\$
    – Faisal
    Feb 27, 2017 at 14:27

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The link topology on your diagram contradicts USB topology. The hub is a host, and PC is a host, and USB does not allow direct host-host communication.

What you might need is so-called "USB Transfer Cable", like this Belkin Model F5U279. It has some sort of USB<->USB bridge, I am not sure what is inside. They claim it operates at HS (480 Mbps) rate, and they are designed for file transfers. However, the link works (has drivers) usually between two identical Windows OS, so I am not sure if Android supports these devices.

Technically there should be PCI/PCIe add-on cards that could go into PC slots and present themselves as USB devices, but for some reason they don't exist, except one very special card that is used in USB-IF certification as a special reference USB device. [ As Tom Carpenter commented, there is USB3380 pripheral controller designed by Broadcom/Avago/PLX, but... "Software development is required. To obtain RDK, please contact PLX Sales Representative or Distributor", which might be challenging]

ADDITION: The "USB Transfer cables" are usually based on Prolific PL-25A1 bridge chip, which essentially is made of two USB devices with FIFO buffer in between supporting bulk transfers.

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    \$\begingroup\$ You can get device<->PCIe cards such as dev kits based around the USB3380, but it's not the sort of thing you would want to set up as the documentation is hard to come by unless you can get Avago to give you access, and there are no real off-the-shelf drivers to speak of. \$\endgroup\$
    – Tom Carpenter
    Feb 26, 2017 at 21:04
  • \$\begingroup\$ @TomCarpenter, yep, you are quite right, here is one example, amazon.com/Bplus-PP3380-AB-USB3380-AB-Evaluation-Board/dp/… just for $208, but developing a driver will likely require some effort, unless it comes with something usable. \$\endgroup\$
    – Ale..chenski
    Feb 26, 2017 at 21:18

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