Dealing with modem hangs

Dealing with modem hangs

[Yevhen Kyriukha]

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I use 3G modems connected to unattended terminals for a long time.
I use ofono for managing 2G connections.

All this time I'm suffering from modem hangs: during establishing 2G
connection modem may hang, i.e. it stops reacting on AT commands to
specific port.
I'd tested a lot of modems of different brands before selecting one.
And I have to say that *every* model has such issue.

So I created a workaround for this (patched ofono):
When I send AT command I start a timer that fires when no response is
received during some timeout. So if timeout is reached I send
AT+CFUN=1,1
command that makes modem reset.
After that modem can be usable again.

I was surprised that ofono doesn't have such functionality.

So I think ofono should have some sort of mechanism to reset the modem
if it stops responding.
What do you think?

-- 
Best regards,
Yevhen

Re: Dealing with modem hangs

[Denis Kenzior]

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Hi Yevhen,

On 03/24/2014 03:45 PM, Yevhen Kyriukha wrote:
> I use 3G modems connected to unattended terminals for a long time.
> I use ofono for managing 2G connections.
>
> All this time I'm suffering from modem hangs: during establishing 2G
> connection modem may hang, i.e. it stops reacting on AT commands to
> specific port.
> I'd tested a lot of modems of different brands before selecting one.
> And I have to say that *every* model has such issue.
>

Most commonly this is a sign that the AT command responses are not 
formatted properly.  Are you running the v250 parser by any chance?  The 
permissive parser is more forgiving.

> So I created a workaround for this (patched ofono):
> When I send AT command I start a timer that fires when no response is
> received during some timeout. So if timeout is reached I send
> AT+CFUN=1,1
> command that makes modem reset.
> After that modem can be usable again.

If the modem responds to AT commands, then the likely cause is something 
else.  Most 'real' hardware deals with true modem firmware crashes 
differently.

>
> I was surprised that ofono doesn't have such functionality.
>
> So I think ofono should have some sort of mechanism to reset the modem
> if it stops responding.
> What do you think?
>

Share the AT command logs of when this happens, maybe there is a simpler 
fix.

Regards,
-Denis