From:
[email protected]
Sent: Thu 5/17/12 8:14 AM
To:
[email protected]
Dear Stephen,
Your service request : SR #{ticketno:[8200488157]} has been reviewed and updated.
Response and Service Request History:
You pretty much nailed it. I was able to get a little more info from the embedded team into borderline-proprietary information, so I'll try to elaborate on what you understood.
TCase for AMD processors comes from a few thermistors (not one, apparently, just found that out) inside the processor case (at the bottom, where the pins are), connecting down to the CPU via the Junction. There are always more than 1 (at least 2, up to 6-8 potentially, but no elaboration given on how many per model), but the TCase temperature is determined by averaging those values out, done by the processor.
TJunction is the temperature where the pins hit the board, and is usually a couple degrees cooler as all 940/941 pins aren't all firing at the same exact time, and not always evenly distributed when only 400 are on at one time.
TCore is actually mathematically guessed based on the varying TCase values,
as there is no way to get a diode on top of the cores inside the processor, and putting it underneath the cores (between the bottom of the case and the bottom of the cores, which hover on a little silicon platform) would yield an inaccurate reading. As such, optimizing the core space on the wafers by keeping thermistors off,
they just mathematically extrapolate the core temperature from the TCase values, based on core location on the processor and the values retrieved in that general area, plus some mathematical calculations.
TJunction is still a diode on the board, under the processor, which most boards still have,
just in case the TCase values (or TJunction value given by Intel processors) are wrong for whatever reason. Though in some cases, TJunction can be off by as much as 20F, so it's obviously not an ideal value. Still, there are a lot of board manufacturers who will still include it, regardless of how necessary, because it's how they've always done things, and if there are problems with new processors or broken thermistors, they can still report a temperature, even if it's not the most accurate.
Sorry for the misinformation about the cores, I really had to get the embedded guys to give a little to get some information confirmation, including the number of thermistors in the case and where this coretemp comes from. A coworker summarized it well by saying that it's so tough trying to get confirmed information, because you get different reports from 3rd parties, and the actual designers/manufacturers want to keep as much information secret as possible. Sorry that this still isn't 100% concrete, but they finally gave in a bit and gave me a bit more information to work with this time, so now you (and I) have a clearer definition at least of what's going on temperature-wise.
In order to update this service request, please respond, leaving the service request reference intact.
Best regards,
AMD Global Customer Care
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