[Ovmsdev] Motor temp does not support negative numbers (car_tmotor)

[Thomas Bergo]

Hi Mark.

it looks like you have forgot to change the car_tmotor to signed int?

>From changes.txt:

# Change car_ambient_temp, car_tpem, car_tmotor and car_tpms_t to signed int


>From ovms.c:

unsigned int car_tmotor = 0; // Tmotor


Regards, Thomas



2014/1/14 Mark Webb-Johnson <mark at webb-johnson.net>

> Reviewing this, I find:
>
> extern signed char car_ambient_temp; // Ambient Temperature (celcius)
> extern signed char car_tpem;         // Tpem
> extern unsigned char car_tmotor;     // Tmotor
> extern signed char car_tpms_t[4];    // TPMS temperature
>
>
> The car_tbattery and car_cooldown_tbattery are already signed int.
>
> I propose to change car_ambient_temp, car_tpem, car_tmotor and car_tpms_t
> to signed int. For the sake of 7 bytes I don't think it is worth the risk.
>
> Code in vehicle_twizy.c is a good example of guarding for this:
>
>       // MOTOR TEMPERATURE:
>       if (CAN_BYTE(5) > 40 && CAN_BYTE(5) < 0xf0)
>         car_tmotor = CAN_BYTE(5) - 40;
>       else
>         car_tmotor = 0; // unsigned, no negative temps allowed...
>
>
> Simplifying code like that will probably save as much flash as we lose in
> going from 8 to 16 bits.
>
> Once we've got over the current compilation flags / space issue with the
> 1.6 firmware, I'll make this change.
>
> Regards, Mark.
>
> On 13 Jan, 2014, at 10:46 pm, Mark Webb-Johnson <mark at webb-johnson.net>
> wrote:
>
> Sound advise.
>
> Given just a handful of temperatures, it is probably least impacting to
> just change to 16 bit signed and put this one to rest. It keeps coming
> back, and it would be good to solve it once and for all. Impact is 1 byte
> extra ram per temperature, plus some flash for the 16 vs 8 bit.
>
> Moving to a 40C offset is tricky to maintain backwards compatibility.
>
> Regards, Mark
>
> On 13 Jan, 2014, at 9:51 pm, Collin Kidder <collink at kkmfg.com> wrote:
>
> I don't think you'd want to do that. 127 deg C really isn't that terribly
> hot and -128C is extremely cold. If it is necessary to retain use of an 8
> bit variable then the standard solution is to just offset the temperature
> stored by -40. That way you can read -40 to 215C which is a pretty
> reasonable range. Unfortunately, I fear such a change would necessitate
> many other changes in code. It might be better to expand to a signed 16 bit
> integer.
>
>
> On Mon, Jan 13, 2014 at 7:50 AM, Håkon Markussen <
> hakon.markussen at gmail.com> wrote:
>
>> Hi (Mark).
>>
>> In ovms.h the motor temperature is defined as unsigned char
>> (non-negative):
>> extern unsigned char car_tmotor; // Tmotor
>>
>> Currently the weather is cold in Norway (-15 C) and I noticed that motor
>> temp was 244C.
>>
>>
>> Is it possible to update the car_tmotor to
>> extern signed char car_tmotor; // Tmotor
>>  in ovms.h?
>>
>> Best regards
>> Håkon
>>
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>>
>>
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