On 07/13/2016 01:27 PM, Harald Welte wrote:
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
Sure, makes sense.
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.
oFono expects modem drivers to guarantee 3 broad states:
disabled (Powered=0, Online=0) - Sim Card off, TX/RX circuits off
enabled (Powered=1, Online=0) - Sim card reader on, TX/RX circuits off
online (Powered=1, Online=1) - full functionality
How the modem handles things like IMSI attach / detach is specific to
the firmware. (Some companies might even consider specifics a secret).
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
That could be just the modems you're picking. Some of the modems out
there have better firmware implementations that others. I think in
general Sierra has a lower quality driver in oFono than say Ericsson or
uBlox. But that can be fixed with a bit of work.
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.
Understandable, but there are no real rules. It all depends on what the
hardware can do. oFono core just sends requests to the driver. It is
up to the driver to figure out how AT channel multiplexing is setup,
etc. Generally the rule of thumb is 1 AT channel for commands + 1
high-speed interface. Or 1 AT channel for commands + 1 for PPP. If
your hardware supports multiple active contexts, then you'd need
multiple high-speed interfaces. Combinations of high-speed + PPP are
also possible. Then some AT modems have dedicated GPS interfaces, etc.
A 100% reliable behavior is important. ofono crashing and
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.
Yep, but sometimes this is something we can't even control. Modem
firmware is notoriously buggy itself.
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.
Understood. But triggering a reset on CFUN=1 is not the way to do it.
In the context of oFono, online_modem is supposed to simply activate
RX/TX circuits + whatever logic in the modem to connect to a network.
enable_modem is supposed to turn the SIM card on.
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.
Can you do it when powering the device down?
>> Examples for this are e.g. the Sierra Wireless SL808x series of modems,
>> 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.
Yep. Properly integrated devices are easier. But then there's no USB
bus in the way. You generally just 'know' that a modem is there. No
hotplug, etc. The modem detection is also more or less static
>> It is somewhat logical, as a +CFUN+1 is supposed to reset _all_ of the
>> 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.
Possible, but Sierra might want to read 27.007. CFUN=1 should not reset
<rst>: integer type
0 do not reset the MT before setting it to <fun> power level
NOTE 2: This shall be always default when <rst> is not given.
It may be that CFUN=1 is simply the wrong command to send for Sierra
> 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 the SIM
> 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.
Absolutely. And oFono supports SIM hotswap. But I've not seen any USB
dongles do this.
The latter functionality is by the way also used in case you work
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
Assuming your firmware supports this. Many just crash if your do a
hotswap. The more reliable approach might be SIM REFRESH, but even that
is kind of nasty and device specific.
Having said that, oFono core has no problems supporting this. How to
make the hardware work reliably is the issue.
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.
Sure, but you're talking about very device specific device detection.
There's nothing stopping you implementing the behavior you want.
Our USB detection is done inside plugins/udevng.c The current logic is
pretty simple. It assumes that if a device drops off the bus, its been
pulled by the user. This works fairly well for our typical use case.
Anything more complex gets really complex. Many device manufacturers
don't even program the usb descriptors properly, so you have no idea
whether the same device was plugged in, a different one, etc.
You can implement any sort of custom detection logic via another plugin.
> If you want proper control of a modem power state, you might want
> 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
Good question. For 'proper' devices which are connected using a
high-speed serial bus or whatever this isn't an issue. It tells us that
it has reset and we can take appropriate actions.
For USB, it just simply has never been a concern. If your USB
descriptors are setup properly, you can use the serial number (or other
unique identifier) to name your device object. Maybe some other
strategies might work. If you get into issuing AT commands to determine
IMEI, etc, it gets complicated.
2) I'm not talking about a full power-cycle in my original
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?
The core has no concept of a bus. The driver tells it when a modem is
created / removed. The driver has to abstract all these details.
Another question: Which (LGA, connectorized) 2G/3G (and possibly 4G)
modems would you recommend in terms of highest quality of ofono driver
Right now I would say Telit or uBlox. The AT commands are generally
available and the firmware is of pretty decent quality. I think some of
the newer Telit/uBlox modems are really an Intel modem, with a slightly
modified Intel firmware, to the point that even most of the AT commands
are the same.
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 :)
Definitely! The more testing the better. I'm happy to support your
efforts as best as I can.