MDC
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Re: overclocking

Tue Aug 02, 2011 4:03 pm

Is it possible to overclock the R-Pi. If so how would you do it. I remember seeing something on the bbc about overvclocking, they did it with liquid nitrogen and another guy did it with water through pipes (like a cooling system).

Michael
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Re: overclocking

Tue Aug 02, 2011 4:07 pm

The thing's not even released yet and you're already talking about overclocking it :rolleyes:

MDC
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Re: overclocking

Tue Aug 02, 2011 4:27 pm

Thats the point isn't it. Do everything with it to see what it's full potential is then do projects with what you have discovered.

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liz
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Re: overclocking

Tue Aug 02, 2011 5:02 pm

We haven't tried. Suggest you go and buy some helium. :)

(In all seriousness, there's 10-20% headroom for overclocking. But as I say, we haven't tried it yet - I expect a full and detailed report from you if you give it a go!)
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MDC
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Re: overclocking

Tue Aug 02, 2011 5:10 pm

Will do.

God I love the smell of burnt raspberries in the morning.
8-)

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ukscone
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Re: overclocking

Tue Aug 02, 2011 5:14 pm

Quote from MDC on August 2, 2011, 18:10
Will do.

God I love the smell of burnt raspberries in the morning

8-)

personally i'm more into underclocking :)

but they could have a whole range of aromas produced when overclocking. you could have the raspberry-pi ceder edition, the raspberry-pi lavander edition (for when you want to de-stress after a long day of bug hunting), the raspberry-pi apples and cinnimon edition. i foresee a whole new marketing campaign

MDC
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Re: overclocking

Tue Aug 02, 2011 6:53 pm

personally i'm more into underclocking

Why not both, as I may buy 2.

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ukscone
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Re: overclocking

Tue Aug 02, 2011 7:07 pm

Quote from MDC on August 2, 2011, 19:53
personally i'm more into underclocking

Why not both, as I may buy 2.



yeah why not. underclock one and overclock the other and they'll average out

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Re: overclocking

Tue Aug 02, 2011 8:41 pm

Quick to mod it lol, I hope it can be over clocked to the 1ghz mark

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Lob0426
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Re: overclocking

Fri Aug 05, 2011 11:37 pm

since the memory board is on top of the processor cooling an overclock could be a problem at the upper end of the clock! is there thermal paste in between the processor and the memory unit?
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Re: overclocking

Sat Aug 06, 2011 7:32 am

Nope, no thermal paste.

The processor unit is a regular cubiod with a grid of tiny balls of solder on the bottom surface (known as a ball grid array package or BGA) and landing pads on the top surface.

To save space on the PCB, some CPUs intended for the mobile 'phone market have pads on the top surface, which allows the memory (also BGA) to be placed directly on top of the CPU. This is known as package-on-package or PoP. This is the type of package Raspberry Pi uses for the CPU.

Each ball on the bottom surface carries one signal between the printed circuit board and the processor and each pad on the top surface carries one signal between the processor and the memory.

This configuration has another advantage in that the signals between memory and CPU are very high speed and challenging to lay out, requiring all the tracks to be (approximately) the same length. Placing the memory directly on top of the CPU elliminates a lot of PCB design complexity.

When the PCB is assembled, the solder balls melt a little, sticking the memory, processor and PCB together mechanically and electronically.

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Re: overclocking

Sat Aug 06, 2011 7:45 am

brilliant technology!
but i hope that you guys will make a model a board with a bigger memory as well.
like an model A v2 since there are some users outside who dont need the second usb and lan port but still leeching for a bigger memory...
just like me ^^ i dont need a nic since i have no use for that. i do all on wifi. but i´d love to have the bigger memory.

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Re: overclocking

Sat Aug 06, 2011 9:42 am

Quote from Michael on August 6, 2011, 08:32
Nope, no thermal paste.


Acutally, that's based on prior experience. I've never heard of PoP chips using thermal paste between CPU and memory but I guess it could be done and can't answer definitively for the R.Pi device.

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Re: overclocking

Sat Aug 06, 2011 1:46 pm

@AmyS3
Yeah sure Eben builds a custom SOC for every user.
I bet this will be cheap and you will save your 50 cents fot that NIC.
You should try to buy a car with one less door as well.

@Michael
Thermal paste could short circuit the ICs on tha PoP.

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Re: overclocking

Sat Aug 06, 2011 3:02 pm

Most thermal paste is electrically non-conductive and would prevent the solder balls making good conduct with the pads if it worked itself into the wrong places, which is why I am doubtful. Even silver grease is only slightly electrically conductive. The PoP chips I am familiar with have pads pretty much completely across the top surface of the CPU chip, which is flat. I guess if the bottom package is more like this then one could in theory but I'm still doubtful.

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Re: overclocking

Sat Aug 06, 2011 3:29 pm

Without the thermal paste any attempt to use a heat sink will be less effective. A heat sink might still have some effect by removing heat from the memory package and increasing the heat dissipation of the underlying processor package. From what little I have read it would be next to impossible to remove the memory package as a DIY project without ruining the processor. I believe thermal paste could be used on the stepped style package but the unit failure rate would be higher, (any paste on a pad it will not seal, as you pointed out) definitely not a way to keep cost down. It still would not hurt anything to try a small heat sink before attempting an overclock. So does a 20% overhead equate to 1.2 GHz? Oops my math sucks sometimes how about 850 MHz
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IRBaboon
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Re: overclocking

Sat Aug 06, 2011 3:30 pm

Thermal paste electrical resistivity can change over time....

Personally i would use superglue.

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Re: overclocking

Sat Aug 06, 2011 10:39 pm

Quote from IRBaboon on August 6, 2011, 14:46
@AmyS3
Yeah sure Eben builds a custom SOC for every user.
I bet this will be cheap and you will save your 50 cents fot that NIC.
You should try to buy a car with one less door as well.

i dont care if the price would be the same of the model b but just without the nic to save energy. thats all.
i have no idea why you think i want to save money that way.. and what the heck got a car to do with that??? seriously

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liz
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Re: overclocking

Sat Aug 06, 2011 10:52 pm

Keep it civil, chaps!
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Re: overclocking

Sat Aug 06, 2011 11:54 pm

i´m sorry.
back to topic.
if i remember correctly i´ve read something that even with overclocking the temperature should not rise in a drastic way, so a small passive heatsink attached with some thermal compound glue on top of the memory should do the trick.
but it seems that we still have to wait for the alphaboards to come back for some testing and temperature sensing. any speculations about overclocking and the generated heat in doing so is currently a bit pointless in my opinion.
but overclocking itself is possible..

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Re: overclocking

Sun Aug 07, 2011 1:40 am

Which do you think will be the ultimate limiting factor, heat or the capabilities of the CPU itself? I mean we've all hit that point where no amount of cooling will let that processor run any faster. As I remember my old 700 Mhz processor stayed (relatively) cool with a dinky old fan. As AmyS3 said above, ultimately we'll have to wait for the board itself and get real numbers off of it, but what's your educated guess?
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Re: overclocking

Sun Aug 07, 2011 3:28 am

im my opinion the limit will be the cpu itself and not the heat.
but since the memory is on top which will generate some heat during the usage as well, it is hard to say.
and i don´t think that you can compare a normal desktop cpu with the arm one.. i had an old 500MHz intel clocked at 660 something MHz without a heatsink at all.. but the size of the processor itself gives enough surface for distributing the heat to the air...
while the surface dimensions of the arm is way smaller..

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Re: overclocking

Sun Aug 07, 2011 3:41 pm

I am sure that the limit will be decided by either the temperature or core voltage. Both of these have always been the deciding factors when trying to establish a stable overclock. I do not have any experience at all with ARM processors, though I assume the over clocking will be along the same paths, multiplier, bus speed or clocking. Bus speed usually effects the memory clock also. I am going to have to do some reading on ARM! Any suggestions?
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Re: overclocking

Sun Aug 07, 2011 8:16 pm

Overclocking is limited by the manufacturing process (TSMC 65GP?).
I estimate 700MHz + 200MHz to 250MHz.

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Re: overclocking

Mon Aug 08, 2011 9:53 pm

Quote from Lob0426 on August 6, 2011, 00:37
since the memory board is on top of the processor cooling an overclock could be a problem at the upper end of the clock! is there thermal paste in between the processor and the memory unit?

No, but the SDRAM is well coupled to the die thermally. In practice, I don't think that cooling is the challenge for overclocking devices like this on 40LP. You can't dial Vdd up very far without frying the chip, and as you push the core speed up your worst paths start to fail *long* before your dynamic power gets to chip-cooking levels.

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