[Ovmsdev] SWCAN and enhanced Ampera/Volt support

Marko Juhanne marko.juhanne at gmail.com
Thu Jul 18 16:14:55 HKT 2019

Hi all,

I've been tinkering with OVMS and Opel Ampera these few past months, and
the I've made some progress with the SWCAN support.

As you know, the SN65 transceiver cannot do High-Voltage Wake Up, so many
of the nice-to-have polling and remote controlling functions are not
available on those cars that rely on it, such as Volt/Ampera. So I've
created an add-on SWCAN board that attaches to the internal OVMS extension
header. The board uses TH8056 transceiver, which is specifically designed
for SWCAN bus. As for the controller, same MCP2515 is used as in OVMS.

Here's the link to the boards GitHub page:

For the firmware patches, here's my OVMS branch:

There are a lot of changes, especially MCP2515 code add-ons and
refactoring, of which some are specific to the new swcan-bus, but some
could be beneficial otherwise as well. Then there's the support for the new
board and TH8056. On the other hand, if a car can be woken up without HV
WakeUp, the board is not really needed and the SN65 can be used with 33.3
kbps speed to communicate on SWCAN bus.

Since ESP32 supports only 3 hardware CS on one SPI bus and all the CS lines
are now already used, there's also patches for software CS (that's what the
additional MCP2515 is using). With my OBD cable I wire SWCAN to use CAN2
lines and put the 2nd MCP2515 on OVMS to sleep, but there's no reason why
all the 4 CAN controllers couldn't work independently at the same time
(untested at this time).

There's also patches to the Ampera/Volt module code base to include SWCAN
support, add handling of several new CAN messages (still work in progress,
more to come!), as well as VoltStar-like capabilities (locking/unlocking
doors, remote preheat) similar to Brian Batista's MyVolStar app/OBDLink
MX-combo. Sadly, I haven't been able to get the VoltStar-specific
functionality to work on my 2014 Ampera, but other non-Voltstar SWCAN
messages do work (waking up the car, controlling windows etc.). This is is
similar to other reports of MyVolStar on 2014 Volt/Ampera, so maybe
something has changed in the ECU behaviour between MY13 and MY14.

It would be really nice to get other OVMS developers with SWCAN/GMLAN
enabled cars to test these. SWCAN specific patches can be tested also
without the board, but naturally the HV Wakeup functionality is not
available.  Let me know if you're interested so I can send a PCB or two for
testing (I have bunch of leftovers).

Best regards,
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