[Ovmsdev] Crashes with streaming mode

[Michael Balzer]

Mark,

I also see the current modem communication layer as a problem source. 
The read buffer only takes 128 bytes, which will not be sufficient for 
many situations -- e.g. a GPS response now needs already two NMEA 
sentences adding up to about 108 bytes -- come in another modem answer 
before the buffer gets handled, and bang we go...

The multiplex mode is quite interesting, didn't know this before -- 
although a really fully asynchronous modem comm handling would not need 
that, I think. But it would need more buffer RAM...

Hm... the SIM908 manual says: "In Multiplex mode, it is recommended to 
use the hardware flow control."

As far as I understand the circuit schemes the current hardware does not 
connect RTS/CTS (pins 66+67) -- right?

Regards,
Michael


Am 30.04.2013 03:28, schrieb Mark Webb-Johnson:
> Michael,
>
> 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.
>
>     http://www.m2m-platforms.com/seminars/2007seminar_material/Telit_CMUX_2_M2M_Platforms_seminar_2007.pdf
>
>
> 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:
>
>     http://www.mt-system.ru/sites/default/files/sim900_multiplexer_user_manual_application_note_v1.3.pdf
>
>
> 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
>> Fon 0202 / 272 2201 * Handy 0176 / 206 989 26
>> <dexter.vcf>_______________________________________________
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>
>
>
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-- 
Michael Balzer * Paradestr. 8 * D-42107 Wuppertal
Fon 0202 / 272 2201 * Handy 0176 / 206 989 26

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