Hi Siarhei,
I measured the temperature of a10 using ds18b20 while set a10 at different
freq.
I think this is a rather rough measurement, because I noticed that a10 has
big cap area(~ 1cm^2 ). but the ds18b20 is in TO-92 package (~10mm^2).
The heat is not evenly spread among the chip surface. the PCB may also act
like a heatsink. i.e. the temperature inside the chip is not the same as
the surface.
Think twice about the RTP sensor, is it actually measuring the core
temperature? Maybe it is placed somewhere far from the core. I have no idea.
Anyway, I carefully glued ds18b20 in the chip center. and I fitted a line
using linear regression.
got
b =[ -198.1115
0.1014]
<https://lh5.googleusercontent.com/-_f728NID9BI/U6BhE9UprxI/AAAAAAAABxg/Xstil8H_URU/s1600/res.png>
some raw data FYR
Freq/MHz ds18b20 a10-raw-reg 1010 53.8125 2480 912 52.625 2468 816
51.75 2464 720 50.875 2457 600 50.125 2447 528 49.6875 2442 408 49 2437
300 48.5 2433 204 48.25 2430 120 48.125 2427
Hope this help.
On Tuesday, June 17, 2014 3:36:21 AM UTC+8, Siarhei Siamashka wrote:
>
> On Mon, 16 Jun 2014 06:03:18 -0700 (PDT)
> Tong Zhang <[email protected] <javascript:>> wrote:
>
> > Hi Siarhei,
> >
> > Thank you for your reply.
> >
> > I attached a ds18b20 thermal sensor on top of a10 to measure the
> > temperature.
> >
> > And I drew a graph using following formula (temp_data-1447)*/20. It
> seems
> > that the two line correlate well on the right(minutes after attached)
> > rather than the left(not long after attached).
> >
> > <
> https://lh3.googleusercontent.com/-VX9j3c6EWnk/U57oUI6gB-I/AAAAAAAABxM/7FfvvskqmzQ/s1600/sensor.png>
>
>
>
> Thanks. While you are at it, can you try to do the measurements for a
> wider range of temperatures? And report the actual numbers for a few
> points. So that we can calculate the correlation coefficient and find
> reasonably accurate linear approximation coefficients.
>
> You can heat up the CPU by using the cpuburn-a8 program as explained at:
> http://linux-sunxi.org/Hardware_Reliability_Tests
>
> And if you set the userspace cpufreq governor, then you can manually
> change the CPU clock frequency. Basically, first you let it idle for
> a while, then get the readings from the a10 temperature sensor (the
> raw number) and the ds18b20 thermal sensor. As a next step you set
> some low CPU clock frequency, run cpuburn for a while and also record
> the sensor information. Repeat this until you reach the 1GHz CPU clock
> speed.
>
> If you also have some A20 hardware, doing the same for it would be
> very interesting too.
>
> This would allow us to finally resolve the temperature sensor
> calibration mysteries.
>
> --
> Best regards,
> Siarhei Siamashka
>
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