Is it possible for one physical USB device to appear as two separate classes of devices?

Question

I'm in the early stages of developing a device that requires a USB connection. At a minimum, the device should appear as an outdated serial port, but it would be useful if it could simultaneously appear as a mass storage device.

Is it possible, or should the device switch between mass storage and communication device, so that is just one at a time?

** [edit] ** I probably fired the question a little quickly; this suggests that this can indeed be done using the USB Composite Device Framework. I would still be wondering if anyone has experience in this regard and there may be some hints or pointers, which platform was used and what if any third-party tools or stacks that they could use.

Answer 1

Yes, you can make the same device as two (or more) logical devices.

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Answer 2

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Answer 3

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I would advise if you intend to master USB development at least a little and you have a USB analyzer - you can not only analyze your own things, but you can also connect a set of other people and see how they are descriptors ...