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Oct 26

Kernel FSB boot option by mifki/semthex

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The default value for FSB is 200 Mhz if you do not specify anything.
So you should check your motherboard spec and the CPU you are using.

I was booting with 200 Mhz but in fact needed 133 Mhz. (Pentium D805 is 533 Mhz).
Thus my clock was too slow, and sound was crap.

Let say your motherboard support 533 and 800 Mhz FSB, but your processor is 533 Mhz.
Then you should set FSB at boot to 533/4 = 133 Mhz.
It is very IMPORTANT that you set the correct FSB speed.

Mifki just released a new version of his 10.4.8 kernel.

Now you can specify the frequency of the FSB as a boot option.

fsb=<mhz>

Download here: www.filefactory.com/file/f618b4

Semthex kernel does also include the possibility at boot to choose a FSB frequency.
The default value is 200Mhz. If you want different value, you have 3 possibilities.

For 100 Mhz: use the -g boot option flag
For 133 Mhz: use the -y boot option flag
For 166 Mhz: use the -z boot option flag

Tips:

Once you know your FSB, you can put it as default value for your boot args. Just edit: /Library/Preferences/SystemConfiguration/com.apple.Boot.plist

You should set this if using semthex kernel and 133 Mhz FSB:

<key>Kernel Flags</key>
<string>-y</string>


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written by skr3dii


7 Responses to “Kernel FSB boot option by mifki/semthex”

  1. 1. semthex Says:
    October 26th, 2006 at 1:20 pm

    Lol, hey skr3dii, my kernel got boot opts for FSB since ages ;-)

  2. 2. BugsBunny Says:
    October 26th, 2006 at 5:08 pm

    - if I have FSB=667, what do I enter? 667/4 = 166?

    - do I enter fsb=166 or fsb=<166>?

    - do I enter it in com.apple.Boot.plist –> Kernel Flags
    <string>-v -x fsb=166</string>

    correct?

  3. 3. skr3dii Says:
    October 26th, 2006 at 6:26 pm

    Hey Bugs!
    It depends if you use semthex or mifki kernel. What you said is correct for mifki. If you use semthex kernel as me, then just use the flag -z for 166Mhz.

  4. 4. dogbert75 Says:
    October 26th, 2006 at 7:06 pm

    I know there isn’t an option for 667Mhz, but wouldn’t 166 be severly slowing down a system?

  5. 5. fred4u Says:
    October 26th, 2006 at 7:53 pm

    as the on-board oscillator run at 166MHz and it’s quad pumped to 667, it will be perfectly fine.

  6. 6. BugsBunny Says:
    October 26th, 2006 at 10:27 pm

    thanks for the clarifications, guys .. :-)

  7. 7. dogbert75 Says:
    October 27th, 2006 at 10:54 am

    Yup…thanks for the info…learn something new every day

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