22.04.2021 02:02, Linus Walleij пишет: > On Wed, Apr 21, 2021 at 10:00 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 > > Oh nice find! > >>> 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. > > Yup there is the bug. (I am guilty.) > > Dmitry will you test & send a patch? I'll send the patch. Thank you all for yours help!
