If I plug in an USB 2.0 device (e.g. mouse, keyboard) into a USB 3.0 port, will the controller still use polling to acquire input data (e.g. keypresses/movements) from the device?
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I have a related question if someone is interested in answering: Maximizing speed of USB 2.0 clients on USB 3.0 hub– KozuchCommented May 15, 2016 at 16:59
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2 Answers
Quoting from Wikipedia:
In USB 3.0, dual-bus architecture is used to allow both USB 2.0 (Full Speed, Low Speed, or High Speed) and USB 3.0 (Super Speed) operations to take place simultaneously, thus providing backward compatibility. Connections are such that they also permit forward compatibility, that is, running USB 3.0 devices on USB 2.0 ports. The structural topology is the same, consisting of a tiered star topology with a root hub at level 0 and hubs at lower levels to provide bus connectivity to devices.
And from "SuperSpeed USB 3.0 FAQ" at Everything Usb
[...] Continuous device polling is eliminated [...] Furthermore, the signaling method, while still host-directed, is now asynchronous instead of polling [...]
answered May 14, 2013 at 22:24
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Thanks. I read something like that, but I wasn't sure if the asynchronous (interrupt based) sampling only applies when a USB 3.0 device is connected, or if it applies with USB 2.0 as well.– MaxiusCommented May 15, 2013 at 0:23
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It only applies to USB 3.0 devices. USB 2.0 devices don't know how to "speak" the USB 3.0 protocol. Commented Feb 6, 2016 at 6:04
Unless the controller is somehow intentionally or unintentionally not backwards compatible the USB 3.0 should be able to "mimic" all the correct aspects of the USB 2.0 controller so that the hardware functions as if plugged into a USB 2.0 port. Continuous device polling was eliminated on USB 3.0 compliant devices because of architecture changes in how USB 3.0 transmits that type of data, not because the capability was simply removed.
