[Ovmsdev] Ioniq 5 - Pushing up some prerequisite changes to components/vehicles

Michael Geddes frog at bunyip.wheelycreek.net
Sun Oct 23 17:38:06 HKT 2022

Thanks Michael,

I have taken it in, and I'll use std::string in poll once code. I guess it
might make sense to convert everything else to std::string.  It wouldn't be
a big task.

 I had just taken out that commit and reworked anyway, and now that you say
it's not the best way of doing things, I'm even happier I made that choice,
as I had intended to possibly make more use of it and won't now.  At the
moment I'm using it to get the VIN (snipped) where I'll try a couple of
times only, rather than continually poll for it.
Hmm... yea - I guess I could do some dynamically created poll table.  Will
definitely consider that.

Further comments inline below:

On Sun, 23 Oct 2022 at 16:15, Michael Balzer <dexter at expeedo.de> wrote:

> Michael,
> what I really dislike about your change is that it adds complexity to the
> underlying function just to fulfill an -- in my eyes more academic -- type
> style choice: having to handle multiple buffer pointers just to provide
> different typing approaches is bad. You could introduce a new construct to
> provide a single polymorphic pointer, but that again adds complexity.
> Agreed, std::string is a bit type-sloppy in depending on char being
> unsigned 8 bit, but that's all to consider, and can easily be enforced if
> ever necessary.
> On the plus side, std::string has far better library support, better
> interoperability (see our use cases), and small string optimization, which
> is especially useful for our platform, as most poll requests and responses
> easily fit into the initial capacity, normally eliminating the need for
> heap allocations.
> So, besides the type independency, I think std::vector has no advantage
> here.
> There's another thing I'd like to address: it seems you're planning to use
> single polls extensively?
> If so, please don't, unless you're also going to do a full rewrite of the
> poller towards a job/worker service task architecture (that's a very old
> todo).
> The single poll utility is really meant for sparse/manual polls outside
> the normal polling scheme. See my comment on the method:
>  * PollSingleRequest: perform *prioritized synchronous* single OBD2/UDS
> request
>  *  Pass a full OBD2/UDS request (mode/type, PID, additional payload).
>  *  The request is sent immediately, *aborting a running poll list
> request*. The previous
>  *  poller state is automatically restored after the request has been
> performed, but
>  *  *without any guarantee for repetition or omission of an aborted poll*.
> This was really meant more for user/script use than for standard vehicle
> polls, though it's OK to use it, where applicable, with caution.
> For all standard polling, install a PID list. You can vary a list by the
> poll state, and you can switch lists if necessary. PID lists can easily be
> generated dynamically, see the VWUP code for an example.
> The place for general CAN utility methods is the
> components/can/src/canutils module, general utility methods go into the
> main/ovms_utils module.
Ahh.. cool.

> Regarding CAN buffer data extraction, there are currently probably as many
> approaches as there are vehicle modules. Certainly would be nice to have
> some standard way here, but won't be simple to rework the existing vehicle
> adaptors.
> The template approach is a nice one for a general solution, but keep in
> mind not every vehicle will use big endian encoding, in some cases not even
> consistently throughout the installed devices.

I had already implemented little-endian and big-endian versions of the data
extract. I will now explicitly mark all of them.

> To be really general, your byte addressing needs to support more than 256
> bytes in the buffer.
Consider that fixed.

> Your templates also lack bit masking and shifting. Some devices use packed
> structs with odd sized bit fields. The DBC engine has support for all this,
> but not generalized. I remember Mark getting a headache from this…
I have a get_bit<>() function and so I would propose it be implemented in a
similar way... ie exract the byte first, then get the bits.
Something like: extract_int<1,2>(byte)  --> Extract bits len 2 starting
from bit 1. We can easily sign-extend that too.

> Regards,
> Michael
> Am 23.10.22 um 02:23 schrieb Michael Geddes:
> Hi Michael,
> Just wanted to say that if you override my objections on the
> std::vector<unit8_t> in the single poll code then I'm fine with that, I
> recognised that it's absolutely your call and that bit has a small impact
> on my code so far.   I can even add versions of the extraction functions
> that use std::string if you want (they would just be inline
> template wrappers around common code anyway so zero compiled cost).
> Also: Is there a better place to put those templated functions?  A version
> of my sign_extend function is already being proposed being used here:
> https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pull/736
> - it would be good if both versions of this function were available in a
> single place.  (There's   sign_extend<UINT, INT>(int_value, sign_bit)  and
> sign_extend<UINT, INT, SIGNBIT>(int_value)  - so they should work fine as
> overloaded template functions).
> I would consider also whether I use std::string in my own code where I'm
> extracting my data out of complete ISOTP poll results. Up to you. That has
> slightly more impact, but the code change is pretty easy.
> //.ichael
> On Sat, 22 Oct 2022 at 07:56, Michael Geddes <frog at bunyip.wheelycreek.net>
> wrote:
>> Thanks Michael,
>> I had already created my commits under the assumption that you would
>> prefer the general changes separate from the vehicle-specific commits.
>> I have created 3 pull requests so far.
>>   1) the bug - that's a no-brainer.
>>   2) 'finalisation' of temperatures and voltages. (Draft, see below)
>>   3) vector poll. This is more a point of discussion (see below)
>> A couple of the next bugs are kind of dependent on the second, so I'll
>> wait until I get that sorted out.
>> More comments below.
>> On Fri, 21 Oct 2022 at 23:31, Michael Balzer <dexter at expeedo.de> wrote:
>>> Michael,
>>> Am 19.10.22 um 07:26 schrieb Michael Geddes:
>>> > Hi all,
>>> >
>>> > I have 6 commits that I would _like_ to get pushed up that are changes
>>> > to components/vehicles required for my Ioniq 5 changes to work.
>>> >
>>> > I can push them all up in a single merge request for review, or
>>> > separate them out into bits.  Some of them I am expecting there to be
>>> > opinions on. I'm prepared to simplify some, and one in particular has
>>> > grounds for nixing. I think it's a good change, but I could manage
>>> > without it.
>>> Please keep PRs as small as possible, focusing on one specific
>>> modification / addition at a time. That way, every merge commit can
>>> easily be reverted if necessary, and changes can be followed and
>>> referred to easily. Especially keep framework changes separate from
>>> vehicle specific ones.
>>> It's also OK to open the PRs tagged as drafts / work in progress, that
>>> helps in commenting on certain parts and tracing refinements. Create one
>>> branch for each PR, pushing new commits into the branch will
>>> automatically update any open PR created from it.
>> Ooh. That's useful. It's been a while since I've used github for collab.
>> Switched the battery sensor P/R over to a draft.
>> >
>>> > One is a simple bugfix - a literal one-character change:
>>> > void OvmsVehicle::BmsRestartCellTemperatures()
>>> >    {
>>> >    m_bms_bitset_t.clear();
>>> > -  m_bms_bitset_v.resize(m_bms_readings_t);
>>> > +  m_bms_bitset_t.resize(m_bms_readings_t);
>>> >    m_bms_bitset_ct = 0;
>>> >    }
>>> Obviously a copy & paste bug, nice find. I wonder how that could slip
>>> through without causing crashes, as there are more voltages than
>>> temperatures in most packs.
>>> Please don't hesitate with opening PRs even for single fixes like this,
>>> the sooner we include them, the better.
>> Yep. Done and understood.
>>> >
>>> > On is a simple code readability change. Using an enum instead of magic
>>> > status values for m_bms_talerts.  Simple enough, but I'm prepared to
>>> > simplify that to a standard enum or get rid of it.
>>> The magic values are simply alert levels, but go ahead, readability is a
>>> good goal.
>>> I'll include it once the Battery Cell code is finalised.
>>> >
>>> > There's some battery related ones where I want to be able to not quite
>>> > know the number of cells from the start and let the OBD responses
>>> specify.
>>> Dynamic pack layout reconfiguration is no issue, I've done that on the
>>> Twizy (look for comments "update pack layout" or calls to
>>> BmsSetCellArrangement*).
>>> BmsSetCellArrangement does clear all the values... which is probably the
>> main thing I was trying to avoid.  Ie- I get to the end and go 'ooh.. only
>> this number of cells were filled in'.  More comments in the P/R about what
>> I want to achieve and fall-back positions.
>> >
>>> > There's also a battery one where the info for the cells have different
>>> > timings (because one has other info), so I want to be able to clear a
>>> > range of cells rather than just reset and start filling the info again.
>>> That may be a bad idea, maybe better to implement some synchronization /
>>> drop readings out of sync.
>>> Reaching a consistent state, the BMS will calculate deviations etc..
>>> Crucial on that part is an analysis of the consistency of the cell
>>> readings to determine the reliability of deviations exceeding thresholds.
>>> See my comments in BmsSetCellVoltage() and list thread:
>>> http://lists.openvehicles.com/pipermail/ovmsdev/2021-February/015079.html
>>> I've skimmed the comments but will read properly and digest.   Yeah it
>> might be best if I just clear the values at the start of the more often
>> running one and then once the other ones come in it will finalise once it
>> gets to the end of those.. so they aren't too far apart.
>>> >
>>> > I've modified slightly the dump for the battery cell
>>> > voltage/temperature, allowing for either or both columns to be visible
>>> > if available. It also copes with the above 'not set' scenario.
>>> Sounds good.
>> I'll push this once the FinaliseCellVoltage pull-request is finalised and
>> accepted.
>>> >
>>> > Finally, the controversial one:  I am using std::vector<uint8_t> as a
>>> > buffer in my ioniq5 code.. and I wanted to be able to use it for the
>>> > polling instead of std::string. I've not replaced the std::string but
>>> > added the ability to have either.
>>> >
>>> > If my aversion to using std::string for binary data is misplaced, then
>>> > I'm ok with the currently small modification to my code that would use
>>> > the std::string version.
>>> The general use case of ISO-TP data is actually dynamic binary strings.
>>> They are meant to and need to be easily aggregated, cut, merged,
>>> partially extracted etc., so they really are strings, not vectors (type
>>> wise).
>> Hmm.. I'm not sure I entirely agree about needing to aggregate/cut/merge;
>> we know the size of the buffer after the first packet comes in so we can
>> pre-set the buffer internal size and append data as it comes in without
>> casting from uint8_t* to char *.  Even if the size is wrong, we can still
>> very easily append to a vector.
>> ON the extraction, I have efficient templated functions that extract the
>> data from the std::vector<uint8_t> buffer.. including to a std::string if
>> required, or to big-endian/little-endian signed/unsigned integers of 1..4
>> bytes with sign-extension now.  These also check bounds so are quite safe -
>> possibly safer than the macros.  The bounds check has already proved itself
>> useful.
>> I have pushed up a draft  request 'single poll to buffer' as it is the
>> easiest way to describe what I want to do.  The first commit is the meat of
>> the change ... but the second is adding all the utility functions.  They
>> probably don't belong in vehicle.h/cpp, but that's easy enough to change.
>> I had them in my ioniq 5 specific code - but have shoved them in there just
>> for a point of discussion.
>> The great thing about the template functions here is that they should
>> expand inline at compile time to quite efficient code.
>>> Regards,
>>> Michael
>> //.ichael
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