How to make an arduino webserver over USB? without ethernet shield nor wifi chip

Question

I would like to begin to understand ethernet handshakes by integrating an Ethernet over USB protocol within an arduino mega or nano. Is there something about the ethernet protocol that requires more components? I know that USB to ethernet adapters exist. In this scenario, it would be more like a USB to arduino webserver experiment, except the arduino webserver would also be providing the IP address to the laptop during the initial handshake.

Shouldnt it be possible to create a simple router from an ATMega2560, where you plug in an arduino to a computer, and the computer is assigned an IP address on the ATMega's network?

Likewise, couldnt you then serve small files from the ATMega to a web browser through this IP connection?

I know this sounds dumb and like over engineering. But i promise i am not crazy and that this could be useful. USB to Ethernet adapters and drivers exist, so i am not sure that there is a hardware limitation. In other words, while ethernet normally requires 4 data lines and USB 2.0 has only 2 data lines, there are still kernel drivers that allow USB to work fine in this way. Likewise the ATMega has only 2 available data lines. So couldnt you begin by simulating a USB to Ethernet device firmware using the ATMega?

A new avenue here that isnt available with Serial connections would be that you could access the ATMega from a web browser, whereas in other driver modes the browser doesnt have the permission to communicate with the Mega.

Why or why not? / How could this be done?

Answer 1

You cannot change what the Arduino's USB does. The USB is not provided by the ATMega2560, but by the USB to UART interface chip.

On a genuine Arduino that may be an ATMega16U2 which could be reprogrammed, but on Chinese clones it most often isn't.

You would need to start with a board that has a real "native" USB connection, such as the Arduino Leonardo (ATMega32U4) or the much more capable (though deprecated) Arduino Due.

Then you would need to create not only the USB "CDC/ECM" device profile, but also the IP stack on top of it to handle the IP data, then a TCP later on top of that to handle the socket data.

The actual CDC/ECM device itself is very simple - much like the CDC/ACM (USB serial) device it's really just a dumb pipe that sends and receives raw Ethernet frames. Interpreting those frames and managing TCP/IP sessions and streams is a far more involved process and would be the bulk of the work. You'd probably want to take an existing standalone IP stack implementation and replace the existing layer 2 code with the CDC/ECM interface instead.

An alternative, as advocated by @Juraj, is to use IP over Serial. This uses a serial protocol (SLIP) to encapsulate the IP frames and has a rudimentary cut-down IP stack in it. However this is old technology and is not well supported by operating systems any more. For example the home versions of Windows no longer have any SLIP support (it used to be provided through "DUNS" - the Dial UP Network Server - which no longer exists).

Answer 2

Try the Web Serial API instead. Example usage.