Heat/ Operationg Temp - Heat Sink

Any technical questions about the Epiphany chip and Parallella HW Platform.

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Heat/ Operationg Temp - Heat Sink

Postby cguy403 » Thu Jul 17, 2014 1:10 am

Within the instruction for applying the large heat sink for the latest batch it has the following text:

1. With this heatsink the Parallella board will function in normal conditions without requiring a fan, depending on your usage. Monitor the temperature using a utility such as xtemp (link below), and keep the board below 70 degrees F. If the board is in a warm environment, or inside an enclosure, a fan will be required to maintain a reasonable operating temperature

but in other posts, I heard 85 degrees C ?, is this just a type in the heat sink instructions , should be OK keeping it below 70 C...

Since I need to run w/o a fan (noise concerns[audible]), I may be able to pump some air across every so often. We probably wont need to run at full tilt and may not need
alot of the FPGA functionality. is there anyway to turn off/ decrease the power/speed of any of the processors to reduce the thermals. ?

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Re: Heat/ Operationg Temp - Heat Sink

Postby FHuettig » Thu Jul 17, 2014 3:09 am

cguy403 wrote:...keep the board below 70 degrees F.

Yes, that's a typo, it should be 70C. And it's the chip temperature, not the board temp, to be more precise. That is a bit conservative as the Zynq timing is done assuming a die temp of 85C max., but we have seen test failures below that number. One issue is that the on-die sensor used by xtemp is not extremely accurate, another is that there could easily be a temperature gradient across the die so the sensor may not be reporting the hottest part of the chip. 70C is safe, go higher at your own risk and monitor closely.

cguy403 wrote:is there anyway to turn off/ decrease the power/speed of any of the processors to reduce the thermals. ?

The only clear & simple way is to use the headless fpga build. Another is to disconnect Ethernet, but for a headless configuration you'll want some way to talk to the board so maybe a WiFi dongle instead. There may be some way to turn off one of the Arm CPUs but I don't know how. It would be possible to create an entirely different FPGA configuration that ran the Arms and SDRAM at lower clock speeds, but clearly that would sacrifice performance and would not be adjustable at run-time.
-- Fred -- Hardware Guy --
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Re: Heat/ Operationg Temp - Heat Sink

Postby zmc » Tue Jul 29, 2014 8:22 pm

This depends a lot on the workload and the environment. In a very cold air-conditioned room, running headless and underclocking the ARM cores using cpufreq-powersave to 222mhz, you can probably get away with no fan. Especially if the cores are idle, and you have enabled the idle-pm in the kernel config.

Mine idles at something like 45C. The problem is that unless you have a very light workload this configuration is not very useful. As soon as you give the arm cores a workload the temperature will skyrocket, even more so if you are driving HDMI and using the ethernet phy. You will have to take a hard look at what you are trying to accomplish with the chip and watch it like a hawk.

I haven't spent any time optimizing the system to be fanless, but I imagine it would be possible. The newer board revisions use a larger heatsink and don't require a fan. There are some other posts that detail ways to trim existing heatsinks to avoid the cap's on the board near the zynq and cool both it and the epiphany.
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