teamtiem
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Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 8:21 am

The Rasberry Pi 4 can overclocked to a maximum of 2147 MHz.
I read somewhere: "In a 32-bit CPU, the largest integer that we can store is 2147483647".
Has the maximum clockspeed something to do with this number?
The CPU is 64 bit but Raspberry Pi OS is 32 bit.

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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 8:39 am

The clock speed was stored in a 32 bit value, so was limited to that number. In the latest firmware it is stored as a 64bit value, so you should be able to go higher if the chip can take it.

This is completely independent of whether the OS is 32 or 64 bit.

Although registers are 32bit in a 32bit SoC, that doesn't mean you cannot have larger 64 bit numbers (or even bigger) - its just requires more instructions to do operations on them as they cannot be done natively.
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teamtiem
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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 9:53 am

Thanks for the answer!

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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 4:13 pm

It appears you can exceed 2.39GHz with the latest firmware. See viewtopic.php?f=63&t=284346
Just beware the OP of that topic has messed up a few details, like "this will void the warranty."
Also I've tried their config, but my Pi4 wasn't stable. Back to 2.0GHz.
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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 4:19 pm

Looks like someone has been watching ExplainingComputers.com video by Christopher Barnatt. Can't access YouTube from work to find it, but he did a Raspberry Pi 4 overclocking video quite recently and the 2147 number cropped up in that.
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teamtiem
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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 4:48 pm

Botspot wrote:
Tue Sep 08, 2020 4:13 pm
It appears you can exceed 2.39GHz with the latest firmware. See viewtopic.php?f=63&t=284346
Just beware the OP of that topic has messed up a few details, like "this will void the warranty."
Also I've tried their config, but my Pi4 wasn't stable. Back to 2.0GHz.
I did some tests. Maximum stable 2200 MHz. Overvoltage=7.

teamtiem
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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 5:19 pm

Mortimer wrote:
Tue Sep 08, 2020 4:19 pm
Looks like someone has been watching ExplainingComputers.com video by Christopher Barnatt. Can't access YouTube from work to find it, but he did a Raspberry Pi 4 overclocking video quite recently and the 2147 number cropped up in that.
What does this contribute to the discussion?

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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Tue Sep 08, 2020 8:42 pm

Maybe not much.

Having another look his 'strange' number wasn't 2147MHz but 2294MHz, so not sure why that number triggered my memory of seeing that video a couple of days ago.

Chris got the 2294 when trying to overclock at 2100MHz. Although the Pi ran his benchmark tests, they were actually slower than when it was set for 2000MHz.

Anyway if it is of interest it is here : https://youtu.be/Ty23K4g1Tyg
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Re: Why is the maximum clockspeed Raspberry Pi 4 2147 MHz?

Wed Sep 09, 2020 2:33 am

teamtiem wrote:
Tue Sep 08, 2020 4:48 pm
I did some tests. Maximum stable 2200 MHz. Overvoltage=7.
That should be qualified as applying to one specific Pi in your possession. How far any given chunk of Silicon can be overclocked has a random component that will vary among individual, specific examples.

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