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Atom Z520PT - SCH US15WPT - ThermTrip# on startup


I am posting this question on behalf of our hardware engineer James. I am the software engineer developing the BIOS for a new Atom embedded design.

Our problem is that the Atom CPU asserts the ThermTrip# signal shortly after initialization. This occurs after the chip-set microcode has started execution, but before the Atom CPU fetches the first instruction.

The board is a custom design based on the Intel Swift Current 2 reference design. Here are the details of the hardware.

  • CPU: Intel Atom Processor Z520PT (512K Cache, 1.33 GHz, 533 MHz FSB)
  • Chip-set: Intel System Controller Hub US15WPT Chipset (Intel SCH US15WPT)
  • RAM: Micron MT47H64M16HR-3 (8 Meg x 16 x 8 banks, 3.0ns @ CL = 5 DDR2-667)
  • The RAM is operated in a single-channel configuration, with four chips to provide 64-bits of data.
  • The memory is soldered onto the board (reference design uses sockets)


  • SCH microcode is SchMicrocode _VLoD2.023x_HiD2015x.bin

We have the following SoftStraps settings in microcode.

  • rank 1
  • tcas 4
  • trcd 4
  • trp 4
  • device density 1024Mbits
  • device Width X16 devices
  • lpc clock loads clk1 = 1, clk2 = 0
  • FSB mode cmos
  • FSB lane reversal not checked
  • split Vtt disable
  • erratum 75 enable
  • erratume 72 enable
  • ddr voltage 1.8V

Here is a bit more detailed description of the problem from our hardware engineer, James. The System Controller Hub starts loading the microcode but stops at ucode address D7FF. Then H_CPUPWRGD from the SCH goes true and ThermTrip# from the processor goes true at the same time. This causes a catastrophic shutdown. I think that the thermtrip# is completely erroneous since the processor is still cold and has been powered on for less than a second. Voltages look good and proper power sequencing has been observed. What could be causing the ThermTrip# ?

Any help is greatly appreciated.



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2 Replies

I assume ThermTrip# signal is between CPU & IMVP chip

ThermTrip# pin is bidirectional & it may be asserted either by processor or IMVP ic.

In my case ThermTrip# pin was false triggered by IMVP IC which was not properly configured for required temperature.

Impact of ThermTrip# assertion cases TM2 to be enabled & processor gets throttled & alway operated at Low Frequency Mode.

I hope the above information be helpful.

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Our hardware engineer solved this problem. It was caused by an incorrect power supply voltage. Thanks for the reply.

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