[Ovmsdev] Leaf canbus

Wed May 7 08:56:10 HKT 2014

Jeremy,

The polling code we have has three states, which control how the polling is done - what is polled, when. The thinking is that we can change the polling behaviour depending on what state the car is in (for example, only polling once a minute or so when the car is charging).

You are correct in that OVMS can connect to either one of the EV or CAR can buses. We would need a custom cable, but that is not too hard.

I guess the advantage of using the EV can bus is that we can directly read the EV can bus values, especially during charging. The disadvantages are that we need to poll the car can bus (but there is very little known about the capabilities of that - I have read that it is possible, but has anyone actually tested it?), and that a custom cable would be required.

The advantages of using the CAR can bus are that the behaviour is well known, and standard cables and tools can be used (we know it works because of leafspy and others). The disadvantage is that the EV bus must be polled (taking care with that 'clicking' issue).

I'm happy to go whichever way you guys think is best. But, if we want to use the EV can bus, we do need to confirm that we can PID poll from that bus through to the car can bus as well as determine the state of the car (off, charging, driving) purely from messages on that one bus.

Regards, Mark.

On 7 May, 2014, at 8:38 am, Jeremy Whaling <jeremy.whaling at gmail.com> wrote:

> Leaf spy uses the car CAN bus because that's the way the ELM modules come stock, so Jim and others did excellent work figuring out how to request from the EV bus presumably through the VCM. Some initial work was done using modified ELM's set up to read the EV bus. Keep in mind the the ELM doesn't have much "horsepower" to filter for specific messages so doing requests is the best way to use it.
> 
> The telematics module in the stock leaf uses the EV bus, and that's the one I'd recommend using for OVMS. When the leaf is off for more than ~30 seconds or so, the Car CAN bus goes silent, even while charging. The ev bus is active when the car is on, charging, remote CC, or for about 30 seconds when the telematics module wakes up the VCM over a separate logic line (I believe pulling a line low). If you start sending requests on the car can while the ev bus is active but the car is not on, you will get a click on/off from a relay for every request you send. It's not damaging but the clicking is obviously undesirable. However if the car is completely powered off and not charging the car does not respond to car can requests. 
> 
> Thus, I don't think using the car can for OVMS is the way to go since most of the time it's use will be when the car is powered down.
> 
> Jeremy
> 
> On Tuesday, May 6, 2014, Tom Saxton <tom at idleloop.com> wrote:
> OVMS reports 0% SOC and sends out panicked low battery messages when it's not getting a valid SOC message from the CAN bus. I get this when I screw up the vehicle setting, which is set via the MODULE command. The first thing I'd do is make sure the vehicle type is set correctly. You can see it from the smartphone app on the Vehicle Info screen, look at the Car line. For my set up I see:
> 
> Car: 2.6.5/TR/V2
> 
> This says the car is running firmware version 2.6.5, the car type is TR (Tesla Roadster), and it's V2 hardware.
> 
> You can get the same info by texting MODULE? to the car, which returns the VehicleID, VehicleType, Units (miles or km), and the notifications setting.
> 
> For the Leaf, you should see NL as the vehicle type.
> 
> Which CAN bus OVMS reads depends on how the cable is wired. I believe the group consensus is that reading from the CAR CAN bus is the best strategy since we know LeafSpy is able to get everything from the that bus.
> 
> The code in vehicle_nissanleaf.c that decodes data from message 0x5b3 looks like it's trying to pull out the Gid values scaled down to work as a rough SOC %, but it looks like the array offsets are off by one. Dividing by 3 is a rough approximation to multiplying by 100 and dividing by 281 to get the standard conversion from Gids to percent.
> 
>     case 0x5b3:
>       // Rough and kludgy
>       car_SOC = ((((int)can_databuffer[5]&0x01)<<1) + ((int)can_databuffer[6])) / 3;
>       break;
> 
> Here's a sample message from our Leaf:
> 
> 5B3 69 BE FF FF FC DD 53 0A
> 
> When I captured that message, I was reading 221 = 0xDD Gids. Both the Leaf message decoder spreadsheet and the OVMS can_databuffer array start indexing bytes at 0, so byte zero is 0x69, byte 1 is 0xBE, etc.  Using the Leaf message decoder spreadsheet, I believe the Gids calculation is: take the low bit of byte 4, shift left by 8 into 16 bits then add byte 5:
> 
>     (((int)0xFC&0x01)<<8) + 0xDD = 0xDD = 221.
> 
> So I think the code to extract Gids from CAR CAN message 0x5B3 is:
> 
>     (((int)can_databuffer[4]&0x01)<<8) + can_databuffer[5]
> 
> My thought is that the Gids value should be stored in car_idealrange. Like Gids, the ideal range on the Roadster is an estimate of the state of charge in absolute energy units. An ideal mile is 225.4 Wh; a Gid is 80 Wh. The UI on the Smartphone app will have to change, or Gids will have to be scaled.
> 
> I propose this:
> 
>       car_idealrange = (((int)can_databuffer[4]&0x01)<<8) + can_databuffer[5]; // raw Gids
>       car_SOC = (car_idealrange * 100 + 140) / 281; // convert Gids to percent
> 
> Optionally, we could do the same thing with Gids that Tesla did to compute ideal miles. The EPA said the Roadster's range is 244 miles, so Tesla equated that with the nominal full capacity of a new Roadster battery, and thus the ideal miles was created. To do the same for the Leaf, take the EPA rating of 84 miles (after Nissan eliminated the 80% charge to get rid of the EPA's stupidity in taking the range to be the average of the 100% and 80% charge levels). After using the raw gids to compute the SOC percent, convert to EPA rated miles:
> 
>     car_idealrange = (car_idealrange * 84 + 140) / 281;
> 
> We can also get the SOH value out of message 0x5B3. According to the spreadsheet, it's the top seven bits in byte one, so
> 
>    soh = can_databuffer[1] >> 1;
> 
> For my sample message above, that's 0xBE >> 1 = 0x5F = 95, which agrees with the SOH reported by LeafSpy when I did that data capture.
> 
> BTW, SOH and Hx appear to be different, but perhaps related. I'm trying to figure that out. I suspect SOH is just the Hx value rounded, but I have some data from the Plug In America Leaf survey which contradicts that. The value in message 0x5BE doesn't have enough bits to be the higher resolution Hx.
> 
>    Tom
> 
> On 5/6/14, 11:39 AM, "Nigel Jones" <nigel at cherrybyte.me.uk> wrote:
> 
> I have the OVMS module running in my car so found an hour tonight to start looking through the source - sorry it's taking a while to catch up, so forgive the newbie questions too......
> 
> One thing I noticed is that I'm getting a 0% state of charge indication, and regular texts saying my battery is low (for testing I setup the sim with unlimited texts.....). I see there was a commit last year which used some of the data from the spreadsheet at 
> 
> https://docs.google.com/spreadsheet/ccc?key=0An7gtcYL2Oy0dGRaSWl6VTV2eXBQMy1ON2xZSzlMUXc#gid=0
> 
> which I found references from the nissan leaf forum discussion at
> http://www.mynissanleaf.com/viewtopic.php?f=44&t=4131&start=340
> 
> If I'm not mistaken the OVMS currently reads the CAR CanBus ? 
> 
> There's an indication in the spreadsheet that CAN message 0x5b3 contains SOC information - but in fact the spreadsheet refers to it as SOH. I have a leafDD and I think this is also known as the Hx figure -- ie it seems to vary with battery age/capacity -- mine for example is down to around 82%, but it is not current state of charge, so I don't think decoding that will help?
> 
> GIDs are what I use in daily driving as they are absolute. The sheet suggests that figure might be retrievable from this message, but then most people would only see a % of 95% for example as life is lost? Is that's what's wanted? I suspect not for the overall SOC figure.
> 
> I can't see much else decoded yet (I was looking for low hanging fruit!) on the CAR canbus - instead most work was done on the EV canbus, including looking at state of charge etc.
> 
> So the question comes how to bridge the data from that bus onto the CAR can. There was reference to this previously on the list at 
> 
> http://lists.teslaclub.hk/pipermail/ovmsdev/2013-October/001712.html
> 
> It would appear the way to get any of the EV can data is to actively request the data. I can see examples of CAN data requests in the tesla module but haven't yet figured how I might for example retrieve CAN msg 0x5bb for example (it's one of the ones to try). I can also see the developers guide p24 which refers to writing on the bus. I'm also wary of the need to be careful in making active requests rather than the easier passive monitoring! Can anyone point me to an example of how I might do this? I'd make that call from the ticker functions? and then handle it in the poll right? 
> 
> Apologies if this is all covered in the nissan leaf forum thread - I have 39 pages to read now...
> 
> Thanks
> Nigel.
> nigel at cherrybyte.me.uk
> 
> -- 
> ----
> Nigel Jones
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