Combine 2 physical devices into one

General discussions about V-USB, our firmware-only implementation of a low speed USB device on Atmel's AVR microcontrollers
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Trashie
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Joined: Tue Apr 12, 2011 4:47 am

Combine 2 physical devices into one

Post by Trashie » Tue Apr 12, 2011 5:23 am

Hello, i'm new to USB and VUSB, so please forgive me if i'm asking something stupid.
Would it be possible to combine 2 physical (usb) devices using the AVR to "look like" just one device to the host?

This is, if:
- All messages from the host are routed to both physical devices
- Only messages from one of the devices are sent to the host.
Would that make both devices "think" they've successfully registered with the host (devices are identical)?

- Then, can i capture reports from both devices, and modify them before sending it to the host?

Thanks in advance,

Alan Chatham
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Re: Combine 2 physical devices into one

Post by Alan Chatham » Wed Apr 13, 2011 2:04 am

I don't know for sure, but I'm almost positive the answer would be no. In order to communicate properly, one of the devices would need to be in direct connection with the PC, and the other would have to be listening to the signals on the data lines without driving them up or down itself, which it would want to do when it tried to send data/communicated. Even if you could get that to work, there's a lot of handshaking and stuff going on, so unless the two devices were sending out their identification data at the exact same time, the 2nd device would be expecting identification handshaking data that it would never receive, and so the 2nd device would probably never come on.

The only feasible way I can see to do what you want to do is to get a chip that has the ability to be a USB host and device at the same time, meaning V-USB isn't right for this application.

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