Mason <slash.tmp@xxxxxxx> writes: > 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, ...) There is a ##thermal channel on freenode that might be a good place to discuss linux thermal framework related queries. > > 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 -- 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
