Quectel UC20: Correct way to get it up and running on embedded?

[Bjørn Mork]

Einar Jón <tolvupostur at gmail.com> writes:
> On 23 March 2017 at 02:42, Dan Williams <dcbw at redhat.com> wrote:
>>
>> RE PolicyMismatch: we're not quite sure what that error represents;
>> we've determined that in some cases it means IPv4 vs. IPv6 mismatch and
>> profiles in the modem, but that doesn't seem to always be the case.
>
> I'm not sure what is causing it, but it's quite easy to reproduce by
> messing with the kernel module (e.g. reloading it):
> $ sudo rmmod qmi_wwan
> $ sudo modprobe qmi_wwan

My best guess is that you experience some mismatch between an
auto-connected bearer and the bearer you try to connect.  But it's a
wild guess.  Try messing with the preconfigured profiles, changing
between IP, IPV6 and IPV4V6 contexts and see if you can prevent the
issue that way.


> I have a couple of other ways to reset the modem, but no easy ones:
> 1)  The Quectel manual says that the command
> AT+QRST=1,0
> will reset the modem immediately, but I don't know how to send AT
> commands to the modem.
> There's no /dev/ttyUSB*, although the device is connected via USB:
> $ mmcli -m 0 | grep devices
>   System   |         device:
> '/sys/devices/pci0000:00/0000:00:17.0/0000:01:00.0/0000:02:08.3/usb2/2-3'
>
> 2) There's also a Control Signal Pin PERST# on the UC20 Mini PCIe board:
> - You can reset the module by driving the PERST# to a low level
> voltage of more than 150ms and then release it.
> Messing with the pins seems a bit drastic...
>
> 3) Rebooting the linux machine also seems to work, but this kills our uptime.


You could try a USB reset.  There is a utility for that in the latest
(yet unreleased) usbutils:
https://github.com/gregkh/usbutils/blob/master/usbreset.c

This will reset the USB device controller, but not necessarily reboot
the modem. So I am not sure it makes any difference in your case.  But
worth trying if you haven't already.



Bjørn