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Thread: Running the WL700gE at 300MHz

  1. #1

    Running the WL700gE at 300MHz

    I've completed my analysis of running the WL700gE at 300MHz. My results were extremely positive.

    With an ambient room temperature of 23.2 C, I measured the following temperatures on the BCM4780 processor:

    Idle @ 264MHz (with gpio interrupt fix): 28.0 C
    99.8% CPU load @ 264 MHz (as shipped from Asus): 29.8 C

    Idle @ 300 MHz: 28.8 C
    99.8% CPU load @ 300MHz: 29.8 C

    As you can see, I measured no difference in temperature between 264MHz and 300MHz when running at high CPU load. The maximum increase in temperature was from idle at 264 MHz to max load at 300MHz. Even in this case, the rise was was only 2 degrees C.

    All measurements were taken after a soak time of at least 15 minutes with a recently calibrated Fluke Model 61 Infrared Thermometer.

    A hi-res picture of the setup is here:

    http://wl500g.info/files/asus/custom...410-201724.JPG

    A similar picture of a slightly cooler reading at 300 MHz and moderate CPU load is here:

    http://wl500g.info/files/asus/custom...410-201744.JPG

    Given this data, I'm convinced it's completely safe, from a thermal perspective, to run the router continuously at 300Mhz with no heatsinking or other modifications.

    So... How does one set the frequency to 300MHz?

    [root@WL700gE ~]$ nvram set clkfreq=300
    [root@WL700gE ~]$ nvram commit
    [root@WL700gE ~]$ sync
    [root@WL700gE ~]$ sync
    [root@WL700gE ~]$ reboot

    That's it.

    Tables within the router, and bootloader, keep the SDRAM timing within spec. Thus far, I've reset the clock on two routers with no ill effects.

    As usual, YMMV. Do this at your own risk!

    - K.C.

  2. #2
    Thanks, working perfect.

    Sollie.

  3. #3
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    Well, the main problem with your measurements is that you've added airflow by removing shieldings and disassembling the case. With my measurements (closed shieldings, closed case) and remote sensor it was more than 50 degress with the same CPU running @264Mhz. This was a WL500gp board with BCM4780CPU. WL700gE should be much more hot due to 3.5" HDD.

    Also, be ware, that according to my experience with upgrading wl500gp memory, some PCBs are not working well @300Mhz - some are failing even to boot. Some guys here reported, that 288 works stable.

    I'm running WL500gp @ 300Mhz for about six months, but I've added rubber based thermointerface (removed from some dead plasma) between CPU and shieldings and a small heatsink on the top of shielding.

  4. #4
    Quote Originally Posted by Oleg View Post
    Well, the main problem with your measurements is that you've added airflow by removing shieldings and disassembling the case. With my measurements (closed shieldings, closed case) and remote sensor it was more than 50 degress with the same CPU running @264Mhz. This was a WL500gp board with BCM4780CPU. WL700gE should be much more hot due to 3.5" HDD.
    Sorry, Oleg, I'm going to have to respectfully disagree with you.

    I have 15+ years experience as an electrical engineer designing embedded electronics. I have spent the last 6 years designing DSP based automotive audio power amplifiers where ambient temperatures regularly exceed 105C. I am very aware how much of an influence even a small amount of airflow can have. I am also very aware of IC failure modes, such as electromigration, brought about by running ICs for extended periods at high temperatures.

    The point of my investigation I found most interesting is that the temperature *delta* between 264MHz and 300MHz was not measurable at high CPU loads. This means that regardless of airflow and ambient environment, the CPU will reach the same steady-state temperature at either speed.

    I completely agree that the final processor temperature will be higher when running in the EMC can with the HDD spinning. However, even with the 50C temperature you measured, there is still 20C of operating margin before reaching the 70C commercial IC maximum temperature spec.

    Furthermore, no matter what the specified temperature range of the IC is (commercial, industrial, or automotive), the only number that matters for IC reliability is the die temperature. To insure long-term silicon reliability, it's imperative to keep die temperatures less than 125C. Since the processor only rose 5C from ambient once power was applied, it's clear this chip was built on a low leakage silicon process. This means that the internal die temperature will not be dramatically higher than the external case temperature. Unlike energy guzzling chips from Intel and AMD, this is normal for energy efficient processor cores like MIPS, ARM and Blackfin.

    Case in point, one of the products I'm designing right now has a processor running at 500MHz. This processor is thermally very similar to the BCM4780. I'd suspect they're both from the same process node at TSMC (Broadcom and the vendor of the processor I'm using both fab at TSMC). My part, being automotive qualified, is specified to an ambient operating temperature of 105C. The silicon is the same. Therefore, even at the commerical maximum of 70C, there's still a large margin before permanent damage to the processor becomes likely.

    Regarding your other points on system stability, you're right. I can't guarantee anything because I don't have the specs for the part. I'd say there's better than even odds that other timing problems could turn someone's router into a brick. Hence the "Do this at your own risk" part of the disclaimer.

    - K.C.
    Last edited by kfurge; 14-04-2007 at 04:15.

  5. Is there a way without rebooting ?

    Thank you very much :-)

  6. #6
    Quote Originally Posted by Gregoire.Favre View Post
    Is there a way without rebooting ?

    Thank you very much :-)
    No.

    - K.C.

  7. #7
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    Quote Originally Posted by kfurge View Post
    The point of my investigation I found most interesting is that the temperature *delta* between 264MHz and 300MHz was not measurable at high CPU loads. This means that regardless of airflow and ambient environment, the CPU will reach the same steady-state temperature at either speed.
    Right and it's in fact so.

    Regarding your other points on system stability, you're right. I can't guarantee anything because I don't have the specs for the part. I'd say there's better than even odds that other timing problems could turn someone's router into a brick. Hence the "Do this at your own risk" part of the disclaimer.
    This was my primary point. You just showed that temperature is OK, and then you've concluded: it's safe to turn on 300Mhz. Unfortunatly there are also some other aspects, such as PCB quality, DDR memory problems and MII switch bus. So, my post was to warn others, that's it's not just nvram changes, but the fastest way to brick this router too... I've not checked wl700ge cfe binary yet, but WL500gp @300Mhz requires 150Mhz at CPU backplane/memory and MII, compared with 132Mhz at @264Mhz.

    We've similar thread in russian thread, regarding WL500gp overclocking, but I've decided not to make it public, as there are some problems with overclocking, including bringing router back to life when something went wrong...

  8. #8
    Sorry for a stupid question, but how can I see current CPU freq?

    In /proc/cpuinfo i see BogoMIPS : 299.82, is it the frequency?

  9. #9
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    Quote Originally Posted by glebushka View Post
    Sorry for a stupid question, but how can I see current CPU freq?

    In /proc/cpuinfo i see BogoMIPS : 299.82, is it the frequency?
    It's related to the frequency. And yes, it's mostly the same for WL700gE.

  10. #10
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    kfurge, could you please run this and post your results for 300Mhz unit?

  11. #11
    Quote Originally Posted by Oleg View Post
    kfurge, could you please run this and post your results for 300Mhz unit?
    May I ask what "this" is? Source would be preferred.

    - K.C.

  12. #12
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    Quote Originally Posted by kfurge View Post
    May I ask what "this" is? Source would be preferred.

    - K.C.
    This tool shows up chip common settings, including core speeds. Source file.

  13. #13
    Quote Originally Posted by Oleg View Post
    You just showed that temperature is OK, and then you've concluded: it's safe to turn on 300Mhz.
    Not to split hairs, but I never claimed it was safe to run at 300Mhz. I said I have successfully run 2 routers at 300MHz and that temperature was not an issue.

    I'll agree that I should have made the warning stronger. Enough said on this issue, I think.

    I've not checked wl700ge cfe binary yet, but WL500gp @300Mhz requires 150Mhz at CPU backplane/memory and MII, compared with 132Mhz at @264Mhz.
    It's the same in the wl700g kernel source I reviewed. Dunno about the bootloader.

    Regarding bad/misconfigured nvram values... It would make sense for the bootloader to check whether or not the nvram reset button is pressed before configuring the clocks. That way, should a bad setting be entered, sane defaults would be applied at power-up.

    - K.C.

  14. #14
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    Regarding bad/misconfigured nvram values... It would make sense for the bootloader to check whether or not the nvram reset button is pressed before configuring the clocks. That way, should a bad setting be entered, sane defaults would be applied at power-up.
    Well, ASUS guys decided not to wire JTAG out of the chip except TCK line... So, playing with CFE is very dangerous, especially at the early stage...

  15. #15
    Quote Originally Posted by Oleg View Post
    Well, ASUS guys decided not to wire JTAG out of the chip except TCK line... So, playing with CFE is very dangerous, especially at the early stage...
    Can you give me a summary of what's been discussed so far on the Russian thread you mentioned earlier? I would like to investigate this 300MHz issue further on the WL700g but I don't want to redo what's already been done.

    - K.C.

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