[Ovmsdev] Crashes with streaming mode

Mark Webb-Johnson mark at webb-johnson.net
Tue Apr 30 09:28:42 HKT 2013


Looking at the design for 3G modules, I noticed something recommended for those modules that seems to be supported for the SIM900 base we use (both SIM900 OVMS v1 and SIM908 OVMS v2). CMUX mode.


This is GSM 7.10 TE-MS multiplexor protocol.

The main problem we have is co-ordinating all the different comms channels of OVMS onto a single serial link to the modem. Incoming SMSes, status indicators, outgoing GPRS TCP data, etc, all run over each other.

The CMUX protocol appears to allow us to have 3 (or 4?) virtual async links, over a single physical async port. We could use one for SMS, another for TCP, and a third for GPS polling. The 3G modules even allow the GPS NMEA data to be streamed back over one of the virtual ports (but I don't think that is available in the SIM908 module we use - hard to tell as the CMUX documents focus on SIM900 not SIM908 [the SIM908 embeds SIM900 and adds GPS]).

It would mean some major restructuring of the comms layer (NET), and we would have to build a small library to encode/decode GSM 7.10, but may be a much more stable approach in the long-term.

SIMCOM seem to implement a subset of the full GSM 7.10 functionality. Here's the manual on it for SIM900:


Regards, Mark.

On 29 Apr, 2013, at 11:48 PM, Michael Balzer wrote:

> Am 28.04.2013 17:06, schrieb Michael Balzer:
>> I just checked in my fix for the USSD reply handler. My tests with streaming enabled did not produce any more crashes, so I think that was the problem.
> I was wrong, it's still crashing. I have to dig deeper it seems.
> Has anyone observed crashes with streaming mode on other vehicles, or is this a Twizy specific bug now?
> Thanks,
> Michael
> -- 
> Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
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