Hi Christophe,
On 02/16/2017 03:26 AM, Christophe Ronco wrote:
Hi,
I use a huawei E3372 modem. It connects to GPRS using PPP. I am able to
activate context and then deactivate it. After that, I am not able to
reactivate the context.
During deactivation, the AT channel used by PPP gets closed and nobody
reopens it. During reactivation, the first AT command (AT+CGDCONT) fails.
Channel shutting down occurs just after NO CARRIER is received on modem
channel (channel is back to AT state) along with a bunch of wrong data.
Here is the log:
Modem: < \r\nNO CARRIER\r\n~\377}#\200!}%}"} }$\210*~
Shutting down is detected in function received_data (gatio.c). Flags
G_IO_HUP and G_IO_ERR are received.
This is a common problem with these devices, a hold-over from olden
serial days. Basically the modem signals a hangup and in addition to
sending a NO CARRIER, it also twiddles with some serial status bits.
This causes the socket to receive a 'shutdown' event. I think that on
some devices the serial port is also physically removed for a short
time, so even opening the port again is likely to fail at least some of
the time.
We use AT&C0 to turn off this behavior, but it sounds like your firmware
is ignoring this.
I have done a patch in huawei plugin that correct the problem at least
with my modem. The idea is for plugin to get notified when modem AT
channel gets closed and when this happens to remove gprs-context, reopen
modem AT channel and restart gprs-context driver. This is possible
because all other drivers (sim, gprs, ...) use PCUI AT channel and not
modem AT channel.
Doing it in the modem driver (e.g. plugins/huawei.c) is the right place.
The fix you have come up with looks okayish. However, you might want
to strace/ptrace ofonod to see what the kernel is actually sending you
to trigger this. Also, a udev event monitor might help to tell if the
tty is being physically removed / reinserted.
We have had a similar fix in the past and it simply didn't work due to
the race conditions outlined.
Regards,
-Denis
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