USB Host device with HUB

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We're currently using a SamD51 as a USB host (full speed) and we're trying to connect a hub to it.

The hub is working perfectly fine and we're also able to connect multiple full speed devices and enumerate them.

But we still have one problem left:

If we connect a low speed device to the hub we have to send a PRE packet to send low speed data from the SamD51 to the hub.

This is defined in the USB spec like so:


PRE packet (tells hubs to temporarily switch to low speed mode)

A hub is able to support low bandwidth devices mixed with other speed device via a special PID value, PRE. This is required as a USB hub functions as a very simple repeater, broadcasting the host message to all connected devices regardless if the packet was for it or not. This means in a mixed speed environment, there is a potential danger that a low speed could misinterpret a high or full speed signal from the host.


If I connect a Hub to Windows with a FS hub you see it here:



The question is: how to send this pre packet using the SamD51?


There is a extended flag but it seems that this is only for Link Power Management:


ENGINEERING CHANGE NOTICE, USB 2.0 Link Power Management Addendum



Last Edited: Mon. Mar 30, 2020 - 02:28 PM