some context - not that it matters much for this discussion -:
In order to test the various Osmocom components implementing GSM/3G
network elements, we are putting together a physical setup with 128
modems and 16 different base stations, all connected over wired coaxial
cables, with digital step attenuators, etc.
The purpose of ofono in this setup is to control lots of modems attached
to a PC, which then runs python software (osmo-gsm-tester) executing a
test suite using the dbus interface towards ofono, as well as various
other interfaces to our Osmocom GSM components.
On the one hand, we want to use plenty of identical modems at the same
time for parallel testing / load testing with reproducible result. On
the other hand, we will be using plenty of different modem models (and
are actually developing carrier boards for 12 mPCIe modems each right
now), in order to test interoperability with as many different baseband
processors, protocol stack vendors, protocol stack versions, etc.
For this to work, we need to make sure that the d-bus interactions on
the modem side actually perform the respective actions on the radio
This is of course a use case for which ofono was not primarily written,
but it is a *very* good candidate, given it's comprehensive dbus
interfaces for virtually every possible feature of a device (not just
the common simple voice call or sms cases, but also including
supplementary services, SIM toolkit, ...
The expectation is that low-level operations like changing the modem
onlie state trigger the corresponding transaction on the network (IMSI
ATTACH / IMSI DETACH). From our experience with ofono and some Sierra
and Gemalto modems, the way how the drivers use the modems does not
reliably guarantee that.
Also, the drivers seem to have tremendous problems with dealing properly
with modem boot-up. Most modems have some unsolicited indications
telling you when the AT interpreter is ready, when the SIM card is
available, when the phonebook has been read, when the SMS have been
At least with those modems tested, ofono did not reliably behave due to
deficiencies particularly in the early start up of a modem, and when
repeatedly going through cycles of enable/online/offline/disable.
So for every modem model we use, we need to clean this up. However,
given that we are not ofono experts, and given that there is no actual
documentation on how the start-up of an ofono driver should deal with
the momdem (which interface should be bound when, in which order, ...)
it has been rather hard.
A 100% reliable behavior is important. ofono crashing and re-starting
due to modem driver interoperability issues would mean that a test case
fails, which in turn means that jenkins will report a test failure on
the respective commit to Osmocom that triggered execution of the test in
the first place.
The first-genreation hardware (not built by us) had 16 SL8082 attached
over UART, using quad-usb-serial chips. Using the USB path one could set
up persistent device names and then bind ofono on top.
The second hardware works with banks of 16 SL8082 modems each, so the
minimal configuration is one ofono process talking to 16 SL8082 over
USB. And here is where the devices disappear from the bus when going
On Wed, Jul 13, 2016 at 12:09:31PM -0500, Denis Kenzior wrote:
The best way to deal with this is not to have the modem reset :) Does
Sierra Wireless have any extensions to turn off this behavior?
But a lot of modems keep internal state unless you fully reset them. So
we actually have a storng incentive to make sure that no state is kept
between two executions of test cases, so doing a real reset actually is
what you want.
Having built devices with GSM/UMTS modems that constantly roam around
the planet abort marine vessels, visiting dozens to hundreds of cellular
networks every month and modems getting locked up in weird states, doing
full modem resets is a very desirable feature in all applications
requiring reproducible/reliable behavior.
> Examples for this are e.g. the Sierra Wireless SL808x series of
> where this behavior is documented and expected. But I'm sure there are
> others, at least I recall having seen this several times in the past.
Generally this isn't done by the modems. Some will physically power off
when you send them a CFUN=0. Then you'd need to replug the USB cable.
Well, if we talk about a consumer-grade USB stick: yes. But as soon as
you talk about industrial/M2M modems, you usually just have to pull the
PWRON pin or something thta is conneted to the pin which usually
connects the PMIC of the baseband processor to the physical on-switch of
the device. All connectorized or solder-type GMS/UMTS modems I've seen
of any vendor offer that option.
> It is somewhat logical, as a +CFUN+1 is supposed to reset _all_
> status in the modem, not just the protocol stack. So the fact that most
> modems don't disappear from the bus afterwards actually means that they
> are cheating.
No, it means they are sane.
I beg to differ, but Sierra and I seem to have the minority opinion
Many modem manufacturers use a second parameter to CFUN, which tells
the modem whether to reset or not. E.g. CFUN=1,1 to cause a full
Sierra has that, too - but the modem is still often performing a full
reset. Probably because they simply want to be safe. Rather reset too
much state, than too little.
I know of no USB based device that provides a complete power down
A complete power-off is actually offered by a lot of modems that I've
seen. My experience is primarily with generations of Sierra Wireless
devices, Gemalto/Cinterion as well as Quectel. And an AT+POWEROFF or
similar proprietary command for a full power-off is often provided.
However, that's not a reset/reboot (with USB enumeration) but a full
physical power off.
Since most of these devices need to be pulled out in order to change
card, it is generally not a problem.
that again may be true for consumer-grade devices, but there re plenty
of modems where a physical card presence pin is actually provided on the
slot, and where you can switch SIM cards.
The latter functionality is by the way also used in case you work with
simulated SIM cards or "remote SIM card forwarding devices", where there
is no physical SIM card present at the device, but just a
microcontroller emulating the SIM card protocol from the ISO7816-4 slave
side. In such cases, when simulating a SIM card swap, you usually just
signal that the SIM slot has opened, and then re-insert a different
But the real reason not to only go to CFUN=4 is becaus again you are
leaking state. The modem is not in the same state as one that has been
reset. The timing and behavior will be different toward the network.
This is just a limitation of USB devices.
I beg to differ. USB devices coming and going on the bus accross device
reset is a well-known phenomenon, and some software can deal with it
very well, while other software less so. There are buggy USB host
controllers, buggy hubs, buggy modems, buggy cables, signal integrity
issues, .... There's EMI that might cause a bus reset, lots of reasons
while devices go and re-enumerate at some point during the life-time of
systems running for more than a day or so.
If you want proper control of a modem power state, you might want to
research devices with full-featured modems on board.
Among other things, we are building such devices. But then, whether
custom-built or existing devices: You will still interconnect the modem
via USB, as a classic UART simply doesn't do for 3.5G or 4G speeds.
But even if you power-cycle the modem physically:
1) how can you make sure the same device always gets the same ofono
device name? It is the same modem, attached to the same port of the
same hub in the same bus hierarchy. This is an issue even beyond our
use case. I've seen USB-attached modems resetting/rebooting
themselves due to software bugs. However, the user application
driving the modem should probably not have to deal with changing
device names in such instances, should it? If there's only one
modem, that might be clumsy but still work. If you have lots of
modems, you never know which one you talk to until you read out the
2) I'm not talking about a full power-cycle in my original question, but
by something the driver issues :)
So if I understand your response correctly, there is no
support/design/concept in ofono that deals with a USB-attached modem
disconnecting and re-connecting to the bus?
Another question: Which (LGA, connectorized) 2G/3G (and possibly 4G)
modems would you recommend in terms of highest quality of ofono driver
btw: Once we have the above-mentioned test setup running, it can be used
the orther way around, too: To test a large number of different modems
with ofono against a Osmocom based GSM network, and use that to test for
regressions in new commits of ofono. So there might be something in for
you, too :)
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)