idProduct=9078 vs idProduct=9079?

1

I have an em7455 which has “suddenly” started misbehaving and I am trying to figure out what is going on. Until this misbehaving started I hadn’t noticed that when the device boots it (usually, but perhaps not always?) announces itself thus:

usb 1-2: new high-speed USB device number 40 using xhci_hcd
usb 1-2: config 1 interface 0 altsetting 0 bulk endpoint 0x1 has invalid maxpacket 64
usb 1-2: config 1 interface 0 altsetting 0 bulk endpoint 0x81 has invalid maxpacket 64
usb 1-2: New USB device found, idVendor=1199, idProduct=9078, bcdDevice= 0.00
usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-2: Product: Sierra Wireless EM7455 Qualcomm
usb 1-2: Manufacturer: Sierra Wireless, Incorporated
usb 1-2: SerialNumber: LF65233321041020
usb 1-2: USB disconnect, device number 40

Notice the idProduct=9078, this seems to be a device for which there are no drivers configured and hence the disconnect at the end. This is then immediately followed by:

usb 1-2: new high-speed USB device number 41 using xhci_hcd
usb 1-2: config 1 has an invalid interface number: 12 but max is 4
usb 1-2: config 1 has an invalid interface number: 13 but max is 4
usb 1-2: config 1 has an invalid interface number: 13 but max is 4
usb 1-2: config 1 has no interface number 1
usb 1-2: config 1 has no interface number 4
usb 1-2: New USB device found, idVendor=1199, idProduct=9079, bcdDevice= 0.06
usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-2: Product: Sierra Wireless EM7455 Qualcomm Snapdragon X7 LTE-A
usb 1-2: Manufacturer: Sierra Wireless, Incorporated
usb 1-2: SerialNumber: LF65233321041020

Notice now it is idProduct=9079 (with description ending … Snapdragon X7 LTE-A) and this device does have drivers which are duly loaded and everything works just fine (in MBIM mode).

However, what has been happening recently (and intermittently, ouch) is that the process gets stuck repeatedly connecting and disconnecting device id 9078 and device 9079 never appears. Which means no internet :roll_eyes:

What is going on? I suspect I’ve got failing hardware but I’d love to hear otherwise!

I’m using this on an HH5a router running Openwrt but for the purposes of trying to debug the problem I’m running on Ubuntu 20.04 with kernel 5.15.0-105-generic from which the syslog excerpts above are taken.

Thanks for reading this far.

2

do you have the AT command communication?
You can check this for the USB PID:

at!entercnd=“A710”
OK
at!usbpid?
!USBPID:
APP : 9071
BOOT: 9070

OK

3

Thanks for that. I get:

at!usbpid?

!USBPID:
APP : 9079
BOOT: 9078

OK

which corresponds with what actually happens.

Why does it announce itself with the BOOT id? Why not go straight to the APP id?

Anyway, I think I now know what the problem is: the length of the USB cable connecting the modem, and the USB power available at the host.

If anyone can suggest a high quality 5m USB cable I will be grateful! I’m trying to source a passive one as an active one might well need drivers installing on the HH5a and might also introduce additional latency.

I’ve upgraded the USB 5V power supply in the HH5a and it works reliably with a 3m cable which is marked “USB 2.0 28AWG x 1P + 20AWG x 2C SHIELDED” but the only 5m cable I’ve got is of a thinner construction and I think that’s where the problem starts. I think I need one with nice thick conductors like the 20AWG in my 3m cable.

I’ve see this one:

https://www.amazon.co.uk/UGREEN-Extension-Extender-Supports-Compatible/dp/B09XHW7D4B

which claims to be USB3 @ 5Gbps so one would think it should do USB2 @ 480Mbps easily enough, but I can find nothing about how it’s constructed, wire thickness, shielding etc.

Any suggestions gratefully received

Thanks

4

Update: the 5m UGREEN cable does not work reliably, keeps dropping out when you drive it at speed. This is surprising as the cable is a thick one so probably has a good amount of copper in it. Difficult to believe this could work reliably at USB 3 speeds. Still searching for a decent quality cable…

5

Update: Eventually realised it is a mistake to buy a USB3 cable if you only need USB2 because a USB3 cable has a couple of additional twisted pairs in there, so, all else being equal, there will be less copper in the original pair which is used for the USB2 comms.

Still, it proved remarkably difficult to find a 5m USB2 cable which was cable of supporting the modem but I did eventually find this one made by Uni:

https://www.amazon.co.uk/dp/B08925X26S

It’s actually 4.5m rather than 5m but I doubt that is the relevant difference - it’s a but thicker and stiffer than the other 3 I tried, all of which worked only until the cable was driven hard, and then errors start and the connection is dropped.

Hope that might help somebody else who finds themselves in the same situation :slight_smile:

6

This cable also turned out to be unreliable so in the end I made up my own cable which works fine. It is documented here https://forum.openwrt.org/t/kern-err-dwc2-not-connected/197800