Hi, Apologies for cross posting. I am running Yocto build image with kernel 4.19.75 on iMX6, the device uses uBlox SARA-R4 4G LTE modem. I have an LTE connection stability issue, it could connect to 4G LTE, then the connection was disconnected between half an hour to an hour randomly, the error messages were qmi_wwan of qmi_wwan 1-1:1.3: nonzero urb status received: -71 and qmi_wwan 1-1:1.3: wdm_int_callback - usb_submit_urb failed with result -19 for errors of EPROTO and ENODEV, many indicated that kind of errors usually caused by insufficient USB voltage. To diagnose it, I changed to use a DC regulated power supply to connect USB voltage from a stable 5V DC regulated power supply, that did help to stabilize the 4G LTE connection, the device has been stable to connect to 4G LTE since yesterday (26 January AEST) morning more than 24 hours which was not able to perform that stability if the USB connected to a laptop or connected the device internal regulated DC voltage from AC power supply. What cannot convince to hardware engineers and what baffling me is that I am also testing an image built from OpenWrt using network manager netifd, it did not have LTE connection issue and it could connect to 4G LTE much stable to use either USB power supply from a laptop or device internal DC voltage from AC power supply. It does not make sense if I say to the hardware engineer that device has power supply issues. Why OpenWrt netifd is much stable than connman / ofono in the same power supply conditions? It seems to me there are subtle differences between connman / ofono and OpenWrt netifd, could the connman / ofono require more rigid stable USB voltage than OpenWrt netifd? Or could the OpenWrt netifd be more superior than connman / ofono in terms of 4G LTE connections? Appreciate your insight comments and advice. Thank you. Kind regards, - jh
