Has anyone successfully connected 100+ Quectel modems to a PC with the Linux driver? I just started on a project that may attempt to use just over 100 EM060K-GL in M.2 → USB adapters. We have validated the M.2->USB adapters work, and I know each USB 3.1 Bus is supposed to be capable of up to 256 devices.
My concern is if the Driver will able to handle that many active instances. I have another 6 weeks before the hardware arrives, just curious if anyone has tested at this scale?
To help others with the same question later on, we made the following discoveries:
There are limits to how many USB devices and USB Serial Ports can be connected to a Linux machine.
Each EM060K-GL creates 4 ttyUSBx ports. The ttyUSB driver can only support 256 ports. Hard limit there of 64
Intel USB 3.0 controllers have a limit of 32 devices (included hubs, onboard devices like bluetooth and wifi) After the overhead you are looking at maybe 15-20 devices/channel. If it has a bridged controller the limit is 64 (again onboard devices and hubs take up some of them)
Some AMD 3.0 Controllers will allow up to 128 devices, Some limit at 64 which after the overhead of 10 port USB hubs(really 3 4 port hubs strung together in an enclosure) we are able to connect 34 modems/channel
USB 2.0 is hit or miss.
Older USB 2.0 controllers handled 128 USB ids.
If you try running off a 2.0 Hub attached to the 3.0 port, many times you are still stuck with the same limitation.
The xHCI Specification says it should be capable of 7096 devices, but in practice it appears that the chipset makers limited the amount of buffer space to account for 32 or 64 devices at the higher rate.
We settled with 34 devices on USB 3.0 and 39 on USB 2.0.