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X99 Taichi Xeon Tjmax
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CPL0 View Drop Down
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    Posted: 13 Feb 2017 at 1:44am
I have recently purchased an Asrock X99 Taichi and while using a retail E5-2683 V3 Xeon processor with it have noticed that the BIOS firmware P1.40 sets it's Tjmax to 92C, P1.50 to 90C while it's actual default is 95C.

What is the reason for this?

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Nobody?

And why is the BIOS changing it without offering it as an option in the BIOS setup?
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Xaltar View Drop Down
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Tjmax determines when the CPU will throttle or shut down due to heat as I am sure you know. If ASRock set it lower or higher than intel's default rating it is likely due to testing and study of the CPU's behavior on that particular BIOS version. Coded changes in the BIOS can drastically effect temps and performance, it is not uncommon for manufacturers to allow a cushion or buffer by lowering the Tjmax limit slightly, this goes a long way to protect your CPU from sudden spikes that could shoot the temps over the Tjmax limit and damage the CPU. 

CPU temp changes have been a lot more abrupt since manufacturing processes have gotten smaller and dies more dense. Where in days of old we would see CPU temps rise say 20c over a few seconds we now see them spike from 30c to 90c almost instantly. The lower than rated Tjmax makes sense in this scenario. 

Out of curiosity, why would you want to alter the Tjmax setting? 
It would only be an issue if you are using inadequate cooling. 


Edited by Xaltar - 18 Feb 2017 at 3:05pm
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Originally posted by Xaltar Xaltar wrote:

Tjmax determines when the CPU will throttle or shut down due to heat as I am sure you know.
Tjmax or "temperature target" is a figure to describe the minimum TCC activation temperature. TCC activation occurs when DTS=0 if TCC offset is 0, Tjmax is used as a means to approximate core temperature. Tjmax is used by some softwares to report core temperature by subtracting DTS from the programmed Tjmax value. Therefore changing this value can result in incorrect reporting of core temperature values. Tjmax has nothing to do with the inbuilt catastrophic shut down temperature.

Originally posted by Xaltar Xaltar wrote:

If ASRock set it lower or higher than intel's default rating it is likely due to testing and study of the CPU's behavior on that particular BIOS version. Coded changes in the BIOS can drastically effect temps and performance, it is not uncommon for manufacturers to allow a cushion or buffer by lowering the Tjmax limit slightly, this goes a long way to protect your CPU from sudden spikes that could shoot the temps over the Tjmax limit and damage the CPU.
The TCC activation offset is used for lowering activation, not the Tjmax value.

Originally posted by Xaltar Xaltar wrote:

CPU temp changes have been a lot more abrupt since manufacturing processes have gotten smaller and dies more dense. Where in days of old we would see CPU temps rise say 20c over a few seconds we now see them spike from 30c to 90c almost instantly. The lower than rated Tjmax makes sense in this scenario.
Lower Tjmax = lower reported temperatures and does not change the temperature point at which DTS=0

Originally posted by Xaltar Xaltar wrote:

Out of curiosity, why would you want to alter the Tjmax setting? 
It would only be an issue if you are using inadequate cooling. 
You've got that back to front. The point is I don't want to alter it, I want to keep the Intel Spec, why has Asrock altered it? One can see the discrepancy when using PECI vs core temp, a 5C difference. 
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Thanks for the correction Thumbs Up

In that case I am not sure, you could try contact Tech Support directly and ask.

http://event.asrock.com/tsd.asp

I have heard the term and seen it about but until now have never really looked into it. My quick google search clearly failed me Embarrassed

I do know that typically TJmax used to only be a fixed value on mobile CPUs (socket 2011 too?), either way I have not encountered any issues regarding it before. Please let us know if you get an explanation, I am sure there will be others wanting to know. Based on your info under reading temps could prove troublesome, even if it is only by +/- 5c.
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I'm not going to chase Asrock up, I'll look into it myself when time permits. Thanks for the reply, appreciated.

Actually the old mobile core 2 duo's had an undocumented DTS calibration register that could be used to change the temperature report. Just a bit of trivia FYI. ;)
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Originally posted by CPL0 CPL0 wrote:

Tjmax or "temperature target" is a figure to describe the minimum TCC activation temperature. TCC activation occurs when DTS=0 if TCC offset is 0, Tjmax is used as a means to approximate core temperature. Tjmax is used by some softwares to report core temperature by subtracting DTS from the programmed Tjmax value. Therefore changing this value can result in incorrect reporting of core temperature values. Tjmax has nothing to do with the inbuilt catastrophic shut down temperature.


Now i see, why if i changed CPU tj max in z490 motherboard on Uefi from Auto i got wrong temperature on each core, it's show me about 80 C - with 0% processor load, and 28 C in package.
How can it fix? Or better using Auto mode ?
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