Thermal info on MBA 1.6 CPU processor - SLA3R

Discussion in 'MacBook Air' started by pughchrism, Mar 20, 2008.

  1. pughchrism macrumors member

    Mar 9, 2007
    Looks like the design spec is 100C. This spec correlates with those who haven't seen core shut-down until >98C. For others, such as myself, I've repeatedly seen shutdowns at 69C.

    At first my CPU temps will run up to mid-upper 70's when viewing HD at full screen. As a test, when I open another HD at full screen then temp goes as high 86C and I start seeing core shutdown. CPU's are maxed-out.

    Temps finally come down to 69C and level off while CPU's continue to be maxed-out and I continue to have core shut-down.

    When I close one of the videos, my temp may drop some more and CPU usage drops to 1/2 or less and I have no more core-shutdown.

    I've used two different temp monitoring programs so I don't think I'm getting incorrect temps being reported.
  2. pughchrism thread starter macrumors member

    Mar 9, 2007
    New Info on Non-temp dependent shut-down on 1.6 processor

    Just found this on an Intel data sheet for this processor (I added some comments).

    If bit 4 of the ACPI Intel Thermal Monitor control register is written to a 1, the TCC (Thermal Control Circuit) activates immediately independent of
    the processor temperature
    . (These next sentences seem to explain the pattern I've seen, in regards to the amount of time my core is off and the amount of time it's on during core shut-down oscillations.) When using on-demand mode to activate the TCC, the duty cycle of the clock modulation is programmable via bits 3:1 of the same ACPI Intel Thermal Monitor control register. In automatic mode, the duty cycle is fixed at 50% on, 50% off, however in on-demand mode, the duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in 12.5% increments.

    If I'm comprehending this correctly, yes, the cores can shut-down independent of temp.

    Looks like apple may need to sort out some of their settings for this CPU. As I read through the Thermal sections on Intel's data sheet for the 1.6 processor, it appears that the different results we are seeing on this forum in regards to when and if core shut-down occurs can all be explained by different parameters Apple is applying to the processor on our MBA's. That seems totally crazy to me. You would think after Apple finished R&D that they would have the settings nailed down tight. But, this data sheet shows to me how different settings in the BIOS, etc. will give exactly the varying results we are seeing in individual units that are all 1.6/80g.

    Here is the address of the data sheet so some of you more knowledgeable people can interpret the Thermal parts of the doc -
  3. NC MacGuy macrumors 603

    NC MacGuy

    Feb 9, 2005
    The good side of the grass.
    Fortunately for me, haven't had a core shutdown yet - and I've tried.

    Hope the ones that do get sorted out.

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