Telit LE910 V2, cdc_ncm and systemd
matthew stanger
stangerm2 at gmail.com
Thu Nov 8 16:38:52 UTC 2018
Hi Carsten,
If it comes to implementing the NCM protocol, it's nice to hear that you
> will guide me :-)
Aleksander gave me some guidance for a similar situation and what you want
to do here is going to be very similar to the
'mm-broadband-bearer-cinterion.c' & 'mm-broadband-bearer-huawei.c' files.
Basically in the 'mm-broadband-modem..' you'll need to have a way to detect
support for Telits's NCM Protocol, such as sending a test read cmd and
checking for a certain response. If that cmd if supported you'll set a flag
to use in the 'mm-broadband-bearer..' to setup the WWAN connection, or
something like that.
On Thu, Nov 8, 2018 at 9:29 AM Stelling2 Carsten <
Carsten.Stelling2 at goerlitz.com> wrote:
> Hi Aleksander,
>
> Thank you for your fast reply, and explanation.
> Meanwhile, I've updated MM to 1.8.2 within my Yocto-Project.
> Also, thanks for your hint to AT#USBCFG=5 (yes, 5 or 3 should work). I'll
> give it a try tomorrow.
>
> Regarding the NCM protocol, I followed the instructions in Telits's NCM
> Protocol User Guide.
>
> AT+CGDCONT=4,"IP","APN"
> AT#NCM=2,4,0,"User Name", "Password"
> Then, I used the output of AT+CGCONTRDP=4, to configure the wwan0
> interface manually. It works.
>
> If it comes to implementing the NCM protocol, it's nice to hear that you
> will guide me :-)
>
> Thanks,
>
> Carsten
>
> -----Ursprüngliche Nachricht-----
> Von: Aleksander Morgado [mailto:aleksander at aleksander.es]
> Gesendet: Donnerstag, 8. November 2018 16:59
> An: Stelling2 Carsten; modemmanager-devel at lists.freedesktop.org
> Betreff: Re: Telit LE910 V2, cdc_ncm and systemd
>
> Hey,
>
> > This is the first time I'm using ModemManager.
> > The type of the modem is Telit LE910 V2 (product ID = 0036), providing
> cdc_acm, and cdc_ncm ports.
> > I'm working on an embedded system, running kernel version 4.9.26.
> > The Init-system is systemd version 232.
> > Actually I've installed MM version 1.6.4 (which comes with Yocto 2.3).
> >
>
> That is an extremely old version, you should definitely try to update. But
> anyway, for the specific issue you're seeing, it would probably be the
> same, see below.
>
> > I can successfully establish a connection to the bearer.
> >
> > The command mmcli -b 0 outputs:
> >
> > --------------------------
> > Status | connected: 'yes'
> > | suspended: 'no'
> > | interface: 'ttyACM0'
> > | IP timeout: '20'
> > --------------------------
> > Properties | apn: '****'
> > | roaming: 'allowed'
> > | IP type: 'ipv4'
> > | user: '****'
> > | password: '****'
> > | number: 'none'
> > | user: '****'
> > | Rm protocol: 'unknown'
> > --------------------------
> > IPv4 configuration | method: 'ppp'
> > | address: 'unknown'
> > | prefix: '0'
> > | gateway: 'unknown'
> > | DNS: 'none'
> > --------------------------
> > IPv6 configuration | method: 'unknown'
> > --------------------------
> > Stats | duration: '300'
> > | Bytes received: 'N/A'
> > | Bytes transmitted: 'N/A'
> >
> > If I start my ppp-on script immediately (within the same second) after
> issuing the command mmcli -m 0 -c -b 0, and receiving the message
> 'successfully connected the bearer', the PPP connection can be established,
> and the configured interface ppp0 comes up. The IP connection works fine.
> >> But, when waiting several seconds (5 seconds or more) between mmcli -m
> 0 -c -b 0 ('successfully connected the bearer') and starting the ppp-on
> script, the PPP connect attempt always fails. Within /var/log/syslog, I can
> see the following messages:
> > pppd[493]: pppd 2.4.7 started by root, uid 0
> > pppd[493]: using channel 1
> > pppd[493]: Using interface ppp0
> > pppd[493]: Connect: ppp0 <--> /dev/ttyACM0
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x081d45a2>
> <pcomp> <acomp>
> > pppd[493]: LCP timeout sending Config-Requests
> >
> > In this case, when opening /dev/ttyACM0 with minicom, I can send AT and
> get back OK from the modem. That surprise me. I would expect that ttyACM0
> is a transparent channel for PPP, and not an AT interface, when
> successfully connected to the bearer. At the same time, I can see MM
> communicating with the modem via ttyACM3 (as expected).
> >
>
> Maybe there's some max time to get PPP up in the tty before it goes back
> to command mode?
>
> > I can't see any dependency to the output of mmcli -b 0 Status IP
> timeout: '20'. Where is this timeout set? Is this the intended behavior of
> MM or do I miss something?
> >
>
> That value is just a "hint" for the upper layers (e.g. NetworkManager)
> about the max time to wait for an IP addressing setup in the data port. In
> reality that value is always 20s except for the very special case of
> satellite comm modems (e.g. Iridium) where 20s for an IP establishment was
> too optimistic...
>
> > Another question I have, is there a way to automatically configure the
> wwan0 (NCM) interface directly, using only systemd mechanisms (no
> NetworkManager involved)? Telit suggests to use the NCM protocol in
> conjunction with LTE connections. Is PPP really a bottleneck for LTE
> connections?
> >
>
> PPP over the TTY is indeed a bottleneck if you want LTE throughput. This
> modem is designed to be used with the NCM interface definitely.
>
> > I've tried
> > [Match]
> > Name=wwan0
> >
> > [Network]
> > DHCP=ipv4
> >
> > but this does not work. Most probably, because the modem LE910 V2 does
> not support DHCP (neither QMI or MBIM). ip shows the wwan0 interface, but
> it is neither configured nor up.
>
> Doesn't have to do anything with QMI or MBIM really. This modem needs an
> AT command to get the modem connected before anything can be sent via the
> NCM interface. ModemManager currently doesn't support the AT+NCM
> combination in Telit modems, but it's just a lack of implementation, no
> other real reason. I actually think I have an old LE910 around somewhere
> here...
>
> Speaking of which, I believe you can change the device to MBIM mode with
> AT#USBCFG=5, have you tried that?
>
> > Does anybody have a working systemd configuration or an idea how to
> achieve this (without NetworkManager)?
> >
>
> Unless you can configure the modem to "transparently autoconnect" and act
> as a router, then you cannot use the NCM interface directly, you need to
> control the modem via AT commands to bring the connection up.
>
> > At least, I miss settings for the PDP context ID to use for a specific
> bearer. With a Vodafone SIM, we have to use a specific PDP context ID to
> access a private APN. Furthermore, the PDP context is different for 2G and
> 4G. Is this an undocumented feature of MM?
>
> The missing AT commands to setup the connection via the NCM interface
> (AT#NCM, AT+CGACT, AT+CGDATA...) would also allow you to configure exactly
> which PDP contexts/EPS bearers to use. E.g you would do something like
> "configure PDP context with cid N with the settings you want" and then
> "connect cid N over the NCM interface", something in those lines.
>
> If you're interested in implementing the AT+NCM support let me know and I
> can guide you a bit if needed.
>
> --
> Aleksander
> https://aleksander.es
>
>
> _______________________________________________
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> ModemManager-devel at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/modemmanager-devel
>
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