Overclocking the XO-1

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Warning

By overclocking the XO-1 laptop you are running the hardware outside the design specifications of both AMD, Hynix, and OLPC. It may fail sooner.

Higher frequency increases heat. The CPU has a heat spreader attached. The RAM does not have a heat spreader. The case does not have a fan. The CPU will skip cycles if it is too warm, and may become slower at higher frequency. The RAM may fail to respond in time.

Underclocking should not cause problems. Power consumption may be reduced. Heat may be reduced.

Overclocking may cause stability problems, data corruption, and possibly hardware damage. As the XO-1 is passively cooled, physical damage could be caused by excess heat. To avoid this, check the heat spreader is firmly attached, increase the frequency slowly, and test the temperature.

A frequency change normally requires a review of operating voltages. The procedure detailed does not change CPU and memory voltages; that would require electrical changes.

How to

First, get to an Open Firmware Ok prompt.

Type the following commands:

ok 4c000014
ok rdmsr
ok u.
ok u.

After this, two hex values will be displayed. Write down the second one that is displayed. For example, this may display 7de009e.

Now you must choose how much to over (or under) clock your CPU and RAM speeds.

The table below lists the value you will need to overclock, and what speeds this value over (or under) clocks the CPU and RAM to.

XO-1 Overclock Settings
in MHz; default is 433/166 (4d9)
CPU Bus Speed
133 166 200 216 233
333 3d3 4d3 5d3 653 6d3
366 3d5 4d5 5d5 655 6d5
400 3d7 4d7 5d7 657 6d7
433 3d9 4d9 5d9 659 6d9
466 3db 4db 5db 65b 6db
500 3dd 4dd 5dd 65d 6dd
533 3df 4df 5df 65f 6df
566 3e1 4e1 5e1 661 6e1

Now it's time to do the overclocking itself.

Type the hex value you wrote down in the previous step into the prompt and press Enter. Then type the overclocking value you chose into the prompt and press Enter.

Next, type the following:

ok 4c000014
ok wrmsr

If it worked, it will appear that nothing has happened. If you have pushed the settings too far your system may have frozen or spontaneously rebooted, just power off and choose a more conservative setting and try again.

Your XO-1 is now overclocked! Keep in mind that this overclock is only persistent until the system is rebooted. Making it permanent was an exercise left to the reader. See Custom_bootloader#Sample_Uber_Bootscript.

References

These instructions were rewritten from a guide posted on the OLPC News Forum. The original guide can be found here.

See also Custom_bootloader#overclock.

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