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

Michael Balzer dexter at expeedo.de
Sun Oct 23 16:15:11 HKT 2022


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 

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 

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 
  *  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.

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.

To be really general, your byte addressing needs to support more than 
256 bytes in the buffer. 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…


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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Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
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