I just learned from goggles AI, that officially USB-modem stick is not supported on the TR1200. I tried a modem, which works on my TR3000 (and on my Windows notebook), actually fails, as it is continously rndis-connecting and disconnecting. Somebody has a trick ?
Sounds like the USB port isn't able to supply the power required by the modem to actually connect to the phone network (many recent modems require more than the 2.5W a standard USB2 port can supply). If so you may be able to work around this with an external powered USB hub (provided that can supply the required power).
Would have been my 1st guess too, but would it be only the RNDIS looping then ?
I don't know much about modem internals but have previously seen this behaviour reported when the USB power supply is inadequate.
not adequate ... Looks like the secret here is the fact, that USB 2.0 specs unfortunately have some variance, delivering UP TO 500mA. I just learned, that a device starts as a low-power device (100mA) and can negotiate for higher power if the host supports it. Seems like the Cudy TR1200 does not do it, which otherwise is a good travel router.
Would be a good idea, to mention this in the openwrt wiki for the TR1200
My guess here is, that the begin of modems transmission activity increases power requirements, which are not met and then connection drops, to trigger a retry.
When it happened to me, the whole thing boot looped, but I guess power reqs differ.
That's kind of true, but not really.
Yes, USB devices must start at 5V, <100 mA and them using more current must be explicitly allowed by the USB controller. This is meant to allow unpowered USB hubs (think 1 USB hub, up to 4 low-power devices, like keyboard, mouse, etc.).
A USB host controller 'should' (read that as must) 500 mA to be compliant though, 5V/ 500 mA - not 510 mA, not 501 mA (and there 'should' be polyfuses against overcurrent/ shorts). So technically the USB controller can still refuse to allow anything above 100 mA, but that wouldn't quite meet certification.
Reality strikes. Neither USB controllers, nor USB gizmos are always specs compliant. There are plenty of USB devices significantly exceeding current limits (all USB HDDs do exceed 500 mA over longer terms, and by a lot during spin-up), devices just bet the house on the unspecified safety margins (USB host controllers on x86 boards tend to serve two ports each, meaning you can 'usually' pull 1 A from them, if you only use a single port - and in practice often even more, because USB devices quickly went beserk, like the aforementioned USB HDDs, USB coffee warmers, etc.).
For embedded devices, these margins are often simply not there at all - compared to the Intel/ AMD/ NEC controllers on typical x86 mainboards you're often dealing with even more (non-spec-compliant quirks, e.g. EM static issues on lantiq). Like the USB HDDs from the days of yore (fast USB SSDs are not that much better, even without the spin-up/ spin-down issues), 'modems' of any kind (DSL, 4g/ 5g, etc.) tend to be quite high on the power scale and dynamic load side, with ripple and other niceties on top.
Do not expect a router USB port to be as battle-hardened as those on x86 mainboards (totally different economy of scale, plug-fest testing, etc.). Do no expect devices to follow specs (heck, we have USB powered soldering irons these days - even if those actually tend be relatively USB-C PD v3.1 specs compiant…).
Thanx for explanation. If possible, pls drop a small warning in the openwrt wiki for the Cudy TR1200.
What should it say?
Note: Some user detected possible power issue on the USB-port, when using a modem stick.
(may be, a link to this thread ?)
I would put that warning on the modem, not the router, you can't say for sure router's to blame for modem (probably) not following specs.
Modem works on TR3000 and notebook. Cudy esp. mentiones USB connection for connection to storage devices.
From AI:
Ăśbersicht mit KI
No, the Cudy TR1200 USB port cannot be used with a 3G/4G/5G cellular USB modem
USB Port Details
- Purpose: The USB 2.0 port on the Cudy TR1200 is strictly designed for connecting external storage devices like USB flash drives or portable hard drives. [1]
If it's AI it got to be correct, but if there's a warning from the vendor we could link to it.
Is this still irony or even sarcasm?
Given the fact that the power requirements of portable hard drives exceed the USB 2.0 specs, it's a daring statement.
If you have, you could try to connect both TR1200 and the modem stick to a powered USB hub and see if the problem still occurs. Just to satisfy the curiosity.
TR3000 has a USB 3 port which, if I remember correctly, should be good for 4.5W (900mA).
Exactly which modem are you attempting to use?
It does, and a ZTE F50 boot loops if you try to hook it up directly to one, without a powered USB hub.
From what I can find, the F50's input power supply is stated as 5V 2A (i.e. 10W) so there's a good chance during startup it draws more than the TR3000 will supply. To be definite would require a USB power/voltage meter - such a device might also help the OP understand his TR1200 problem.
Apparently some GL-MT3000s don't like the F50 either.