[Ovmsdev] Twizzy Rental Service

Michael Balzer dexter at expeedo.de
Tue Mar 8 17:02:53 HKT 2016

Thanks, Mark, great work!


Am 08.03.2016 um 09:24 schrieb Mark Webb-Johnson:
> An update on SIM808. It is just a stop-gap 
> solution, but it buys us some time.
> The changes I’ve made / problems I’ve had:
>  1. Power button needs to be held for 1 second
>     to power down/up the modem (SIM908 was much
>     faster). Not a bad issue, but it did waste a
>     week going back and forth trying to find the
>     cause.
>  2. The SIM808 doesn’t echo LineFeed characters.
>     That is a pain for DIAG mode console, but
>     doesn’t affect anything else. Only
>     workaround possible is to use a terminal
>     program that can map CR->CRLF, or CF->LF
>     (and live with the horrible display in DIAG
>     mode). We’ll just develop on SIM908 modules
>     or use a fancy terminal emulator. I guess if
>     people are using scripts to talk to DIAG
>     mode, they may need some tuning if they are
>     expecting CRLF and just getting CR now.
>  3. GPS initialisation (this is the biggy - more
>     below).
>  4. Build profile in version string. This is
>     just a simple fix to include a #define in
>     the build profiles, and to include that
>     where we show the version string. It means
>     that as well as the version of firmware, we
>     can now see the build profile. Helpful for
>     support of new users.
> The biggest issue has been with GPS initialisation.
> Looking at the current code:
>     // Using internal SIM908 GPS:
>     rom char NET_INIT1[] =
>     rom char NET_REQGPS[] =
>     "AT+CGPSINF=2;+CGPSINF=64;+CGPSPWR=1\r";
>     #else
>     // Using external GPS from car:
>     rom char NET_INIT1[] = "AT+CSMINS?\r";
>     #endif
> So, if the build profile includes 
> OVMS_INTERNALGPS (ie; one or more vehicles in 
> the profile require GPS), then we use a big 
> sequence of initialisations 
> "AT+CGPSPWR=1;+CGPSRST=0;+CSMINS?\r”. We have 
> two issues with this:
>  1. We’re powering up the GPS, even if the
>     actual vehicle we selected doesn’t need
>     SIM908/808 GPS. That costs watts - and with
>     my new fancy bench power supply I got for
>     OVMS v3 development (ok, cheap chinese ebay)
>     I can now see exactly how much ;-).
>  2. The SIM808 randomly doesn’t
>     like AT+CGPSPWR=1 and in particular seems to
>     hate it 100% of the time it is included with
>     other options. You get an ERROR response
>     back from the modem, and as this is done in
>     NET_STATE_DOINIT, it looks like a SIM card
>     error (but is nothing to do with SIM card).
>     We just never saw AT+CGPSPWR=1 fail on SIM908.
> Now, as well as the #defined OVMS_INTERNALGPS to 
> enable the SIM908/808 GPS, we’ve also got 
> NET_FN_INTERNALGPS in net_fnbits which is set 
> during vehicle module initialisation. The first 
> brings in the code, the second should turn it 
> on. Except it doesn’t. The first one turns it on.
> Accordingly, I’m having to change the net.{h,c} 
> layer to split off GPS initialisation into its 
> own states and use a simple AT+CGPSPWR=1 for 
> vehicles that require SIM908/808 GPS and 
> AT+CGPSPWR=0 for vehicles that don’t. I’ve taken 
> the opportunity to switch from 
> using OVMS_INTERNALGPS to using 
> NET_FN_INTERNALGPS in net_fnbits as the decision 
> as to whether to power up the SIM908/808 GPS or not.
> Building and testing that has taken me the most 
> time. It is almost done, and I should be able to 
> commit the code soon.
> Production firmware then goes to the 
> manufacturer in China, and we give the go-ahead 
> for the production run. We should have the 
> modules back in stock towards the end of March / 
> first thing in April.
> Regards, Mark.
> P.S. I can actually recommend that cheap(ish) 
> chinese ebay power supply. It’s available from 
> various eBay sellers, or banggood 
> <http://www.banggood.com/CPS-3205C-0-32V-0-5A-Portable-Adjustable-DC-Power-Supply-180-264V-p-974495.html>. 
> Controls are precise, output is rock solid, 
> ammeter is as accurate as my multi-meter, and it 
> is built like a tank.
> _______________________________________________
> OvmsDev mailing list
> OvmsDev at lists.teslaclub.hk
> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev

Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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