Re:Logic board with 20 USB3 ports
by bsder on Monday September 21, 2020 @06:20PM
(#24549074)
This is unlikely for USB 2.0 and up.
It might be true if you have old devices, though. If you have USB 1.0/1.1 full speed HID devices you can overcommit the available bandwidth for a human interface device. HID devices generally require that they be serviced every 1ms with a 64 byte packet. You might overrun that if you put enough old devices together on an old hub. It's quite unlikely for USB 2.0+ with anything High Speed.
The only issue with new devices is that USB 3.0+ requires twice the endpoints of USB 2.0. The problem is that the Intel controller chips allocate the same amount of memory for USB 3.0 as they do USB 2.0. So if you have a system with a lot of devices (96+), you can hit the memory limit of the controller.
We hit that limit with a 192 device system. It took a while to figure out what the heck was wrong.
It might be true if you have old devices, though. If you have USB 1.0/1.1 full speed HID devices you can overcommit the available bandwidth for a human interface device. HID devices generally require that they be serviced every 1ms with a 64 byte packet. You might overrun that if you put enough old devices together on an old hub. It's quite unlikely for USB 2.0+ with anything High Speed.
The only issue with new devices is that USB 3.0+ requires twice the endpoints of USB 2.0. The problem is that the Intel controller chips allocate the same amount of memory for USB 3.0 as they do USB 2.0. So if you have a system with a lot of devices (96+), you can hit the memory limit of the controller.
We hit that limit with a 192 device system. It took a while to figure out what the heck was wrong.