Source of buzzing determined for hp tc1100

Source of buzzing determined for hp tc1100

[Joshua Wise]

Hi all,

Okay, so I have determined the source of the buzzing for the hp tc1100, 
and I have a list of conditions to be met for the buzzing to show up. I 
determined the following mostly by observation. To determine which ACPI 
modules were causing issues, I whipped up a GOK keyboard to use pen 
input to determine the problem-causer. I will make that keyboard 
available on request.

So, without further ado, here are the conditions to be met:
   * The system must be idle/
   * The system must be undocked from the USB keyboard base.
   * The system must be unplugged from 18VDC power.
   * The processor module must be loaded.

If all of the above conditions are met, the system will emit a buzzing 
from the CPU fan area. (Sometimes the system must be throttled above 75% 
for the buzzing to occur.)

Has anyone any insight?

joshua


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Re: Source of buzzing determined for hp tc1100

[Nate Lawson]

Joshua Wise wrote:
> Hi all,
> 
> Okay, so I have determined the source of the buzzing for the hp tc1100, 
> and I have a list of conditions to be met for the buzzing to show up. I 
> determined the following mostly by observation. To determine which ACPI 
> modules were causing issues, I whipped up a GOK keyboard to use pen 
> input to determine the problem-causer. I will make that keyboard 
> available on request.
> 
> So, without further ado, here are the conditions to be met:
>   * The system must be idle/
>   * The system must be undocked from the USB keyboard base.
>   * The system must be unplugged from 18VDC power.
>   * The processor module must be loaded.
> 
> If all of the above conditions are met, the system will emit a buzzing 
> from the CPU fan area. (Sometimes the system must be throttled above 75% 
> for the buzzing to occur.)
> 
> Has anyone any insight?

This is a faq, the answer is C3.

-- 
Nate


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Re: Source of buzzing determined for hp tc1100

[Jeff Pitman]

On Tuesday 07 December 2004 07:11, Joshua Wise wrote:
> Has anyone any insight?

I still think it's thermal.ko, but i've got it statically compiled in 
here.

It's been reported before for Dell:
http://seclists.org/lists/linux-kernel/2003/Dec/1037.html

I'm going to recompile as module tonight and play around with the 
throttling. I think most people have too much ambient noise in their 
work areas to hear it.  Otherwise, this has got to be happening all the 
time.

-- 
-jeff


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Re: Source of buzzing determined for hp tc1100

[Joshua Wise]

> This is a faq, the answer is C3.

Hrm. I looked in the Intel FAQ linked off of the ACPI.sf.net page, and 
didn't find anything there.

I then googled for acpi c3 noise, which gave me some information about 
Thinkpads and sound card noise, but the noise occurs regardless of 
soundcard-osity. In fact, it seems to be coming from near the CPU fan.

I did do a quick test, though. I did a while true; do sleep 1; cat 
/proc/acpi/processor/CPU0/power; done .

While the system is connected to the USB keyboard, the it will never go 
into C3 state, and bus master activity is always ffffffff.

When the system is disconnected, it will stay in C3 state most of the time.

However, when I connect AC power, the buzzing goes away, but the system 
still spends most of its time in C3 state.

I'm willing to believe that the battery's power supply in combination 
with some CPU supply element causes buzzing, and that the [more|less] 
filtered DC supply does not cause this buzzing. This begs the question, 
though - is there really a power savings advantage to C3? Am I missing 
out on something when I am not in C3 state? Will the device run 
noticably cooler/have noticably longer battery life when C3 state is 
enabled?

I have also noticed that C1 state is rarely entered on this device - 
only 10 usage units over about two hours of uptime. The machine feels a 
bit latent otherwise... I'm not certain whether this is due to the lack 
of C1 state usage, or whether this should just be attributed to the fact 
that the machine is a bit underpowered.

joshua


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Re: Source of buzzing determined for hp tc1100

[Joshua Wise]

> I still think it's thermal.ko, but i've got it statically compiled in 
> here.
Well, recall that thermal.ko depends on processor.ko. rmmod'ing one 
implies rmmod'ing the other.

> I'm going to recompile as module tonight and play around with the 
> throttling. I think most people have too much ambient noise in their 
> work areas to hear it.  Otherwise, this has got to be happening all the 
> time.
The buzzing is actually fairly loud on this device - I can hear it in a 
moderately noisy bus. It's definately audible over the fan (which seems 
to be constantly running when the display is on on this thing...).

I'd get a recording of it, but of course the noise goes away when I try 
to record using the internal sound card. I assume that is for the same 
reason as the USB causing the buzz to cease. Perhaps later, I will fire 
up my big desktop and record from there.

joshua



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Re: Source of buzzing determined for hp tc1100

[Jeff Pitman]

On Tuesday 07 December 2004 07:54, Joshua Wise wrote:
> I then googled for acpi c3 noise, which gave me some information
> about Thinkpads and sound card noise, but the noise occurs regardless
> of soundcard-osity. In fact, it seems to be coming from near the CPU
> fan.

This is not coming from the soundcard on my Thinkpad T30.  It's from the 
thermal unit located around the CPU fan on the upper left of the unit.

> While the system is connected to the USB keyboard, the it will never
> go into C3 state, and bus master activity is always ffffffff.

I have a USB external HD connected and it stays in C2 all the time.

> However, when I connect AC power, the buzzing goes away, but the
> system still spends most of its time in C3 state.

Whether I'm on AC or Battery, it's always in C2.  Usage for C3 is 
extremely low.  AC or Battery there's still buzzing.  Albeit, mine is 
very quiet.

take care,
-- 
-jeff


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Re: Source of buzzing determined for hp tc1100

[Nate Lawson]

Jeff Pitman wrote:
> On Tuesday 07 December 2004 07:54, Joshua Wise wrote:
> 
>>I then googled for acpi c3 noise, which gave me some information
>>about Thinkpads and sound card noise, but the noise occurs regardless
>>of soundcard-osity. In fact, it seems to be coming from near the CPU
>>fan.
> 
> 
> This is not coming from the soundcard on my Thinkpad T30.  It's from the 
> thermal unit located around the CPU fan on the upper left of the unit.
> 
> 
>>While the system is connected to the USB keyboard, the it will never
>>go into C3 state, and bus master activity is always ffffffff.
> 
> 
> I have a USB external HD connected and it stays in C2 all the time.
> 
> 
>>However, when I connect AC power, the buzzing goes away, but the
>>system still spends most of its time in C3 state.
> 
> 
> Whether I'm on AC or Battery, it's always in C2.  Usage for C3 is 
> extremely low.  AC or Battery there's still buzzing.  Albeit, mine is 
> very quiet.

Perhaps my previous email wasn't clear enough.  If you search the 
archives for "noise C3", you'll find more about it.  It's capacitor 
noise due to stop GNT.  Changing the kernel timer frequency (kern.hz on 
FreeBSD) will change the rate.  I use 100, which is not audible.  The 
normal rate of 1000 hz is a very audible tone.  So either disable C3 or 
change your HZ rate to something not audible.

-- 
Nate



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