On 29/04/2015 15:47, Mason wrote: > On 28/04/2015 13:27, Mason wrote: > >> The SoC I'm working on provides a temperature sensor (NXP) in the CPU block. >> The sensor seems to be very primitive, so I wanted to ask experienced people >> what would be the best way to use it from Linux. >> >> General Description >> "The sensor generates an output signal that indicates if the die temperature >> exceeds a programmable threshold. This makes it particularly suitable for >> detecting overheating." >> >> So it seems that the original purpose of this sensor was to periodically >> check that the temperature has not exceeded a given threshold. >> >> - Is the CPU temp higher than 100°C ? >> - No. >> - OK. Business as usual. >> >> (1 second later) >> - Is the CPU temp higher than 100°C ? >> - Yes. >> - Uh-oh! I need to do something about it. >> >> >> Basic Functions >> "The temp sensor uses a bandgap type of circuit to compare a voltage which >> has a negative temperature coefficient with a voltage that is proportional >> to absolute temperature. A resistor bank allows 40 different temperature >> thresholds to be selected and the logic output 'out_temperature' will then >> indicate whether the actual die temperature lies above or below the selected >> threshold." >> >> The available thresholds seem to be chosen somewhat arbitrarily: >> >> -45.1, -39.7, -33.7, -29.4, -24.4, -20.4, -15.4, -10.1, >> -6.4, -1.4, 3.6, 7.6, 12.9, 16.6, 20.6, 25.6, 30.9, >> 34.9, 38.6, 43.9, 48.9, 52.9, 57.9, 61.9, 66.9, 70.9, >> 76.3, 81.3, 85.3, 90.3, 95.3, 98.9, 102.9, 108.3, 111.9, >> 117.3, 122.3, 126.3, 131.3, 135.3, 139.3 >> >> The spacing between values seems arbitrary also. >> (Is there an underlying physical explanation?) >> >> I'm not sure that there is much point in testing for temperatures lower >> than 50°C ? (I'm told that the SoC can reliably function up to 125°C.) >> >> Do higher temperatures shorten the lifespan of a component? >> In other words, would a CPU running 24/7 at 100°C "break" sooner >> than one running 24/7 at 50°C ? >> >> >> Characteristics >> >> Symbol Parameter Min Typ Max Unit >> >> (Operating conditions) >> Tjunc Junction temperature -40 25 125 °C >> Vdd Supply voltage 1.0 1.1 1.26 V >> >> (Normal operating mode) >> Idd Supply current 50 60 μA >> Vbandgapref Ref output voltage 0.72 0.8 0.88 V >> ∆outtemp Absolute Temp ±2 ±10 °C >> threshold error >> T_res Temp resolution 3 4.5 7 °C >> >> >> Given the semantics of the temperature sensor hardware block, I was >> tempted to implement something along these lines: >> >> Create a kernel thread that runs periodically (e.g. every second) >> to check if the temperature is above 100°C. >> - If not, do nothing >> - If yes, somehow prevent the CPU from using the highest frequencies >> defined in cpufreq's freq table >> (They are 1000, 500, 333, 200, 100 MHz) >> >> Is that a sensible approach? >> Is there a way to implement this using the thermal framework? >> >> Or am I looking at this wrong, and things should be done a >> different way? (I'm using 3.14 by the way.) >> >> I suppose I could perform some kind of binary search to zoom in >> on the current threshold (although it might change during the >> measurements, so I'd rather not go there.) > > I'm aware that I posted many questions. I'd be grateful if someone > would answer even a tiny subset. That would get the ball rolling. > > If I understand correctly, if I want to use the CPU throttling > framework, I need to define a "thermal zone device" and a > "cooling device". AFAIU, the cooling device is taken care of > by cpu_cooling.c > > cpufreq_cooling_register(cpu_present_mask); > > My temperature sensor would be the thermal zone device? > How do I tie the two devices together? > Is that where a thermal governor comes in play? > > I took a look at the dove_thermal driver, because it seems simple > enough to understand (by me). > > Looking at ti-soc-thermal/omap?-thermal-data.c > the lookup table looks familiar. Are they using the same kind > of technology as my primitive sensor? (bandgap) > I do note that the precision is much higher though. Hello everyone, Is there, perhaps, a better place to discuss these issues? (IRC, web forum, other mailing list, Stack Overflow, ...) Regards. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
