21.04.2021 23:04, Andy Shevchenko пишет: > On Wed, Apr 21, 2021 at 11:02 PM Andy Shevchenko > <andy.shevchenko@xxxxxxxxx> wrote: >> >> On Wed, Apr 21, 2021 at 11:00 PM Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: >>> On 4/21/21 9:41 PM, Andy Shevchenko wrote: >>>> On Wed, Apr 21, 2021 at 10:05 PM Andy Shevchenko >>>> <andy.shevchenko@xxxxxxxxx> wrote: >>>>> On Wed, Apr 21, 2021 at 1:14 PM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: >>>>>> On Tue, Apr 20, 2021 at 11:26 PM Dmitry Osipenko <digetx@xxxxxxxxx> wrote: >>>>>> >>>>>>> I found a non-kernel example >>>>>>> which uses a similar equation [1], but in a different form. The main >>>>>>> difference is that the Arduino code interprets a raw temperature value >>>>>>> as a signed integer, while upstream assumes it's unsigned. >>>>>>> >>>>>>> [1] >>>>>>> https://github.com/blaisejarrett/Arduino-Lib.MPU3050/blob/master/MPU3050lib.cpp#L111 >>>>>> Oh that's nice. Room temperature as mentioned is 20 deg C >>>>>> I think? >>>>>> >>>>>> The divide by 280 part seems coherent in all examples. >>>>>> >>>>>>> Still, even if assume that the raw temperature is a signed s16 value, it >>>>>>> gives us ~35C in a result, which should be off by ~10C. >>>>> Actually here [1] it says in chapter 3.1 that room temperature is 35°C. >>>>> >>>>> Range: -30°C .. +85°C >>>>> Sensitivity: 280 LSB/°C >>>>> Room temperature offset: 35°C = -13200 LSB >>>>> >>>>> [1]: https://www.cdiweb.com/datasheets/invensense/mpu-3000a.pdf >>>> >>>> So, if I'm reading this and the register description right the value >>>> is in the range >>>> -32768..32767. >>>> -13200 defines 35°C >>>> >>>> 50000 as mentioned by Dmitry is actually -15536. So, it means that the >>>> more negative a value is the higher temperature is shown. >>>> >>>> Since it's linearized scale, now we can see that >>>> >>>> (13200 -15536)/280 + 35 gives us 26.66. >>>> >>>> Does it make sense? >>> (13200 + x)/280 + 35 = (23000 + x)/280, which is what is in the driver. >>> So the only bit missing is the cast to s16. >> >> Cool! So, that cast needs a very good comment then :-) > > "will need" (since it's not yet in upstream) > > The exact value I'm getting is 52144, which is -13392 and gives us 35C. I see that the datasheet says it should be a temperature of the sensor die, so maybe it's a correct value, although it means that it's warm as much as ARM CPU core, which is questionable to me whether it's a correct value.
