- Mar 11, 2000
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See here.
IBM's G3 750FX CPU Software Overclocking?
(iBook 2002 Owner Report @800MHz) - (*Updated with a correction and more info from the reader*)
About a week ago a reader wrote that the IBM 750FX CPU used in the new 2002 iBooks have a bus/cpu multiplier that can be set via software. (The bus/cpu ratio that determines CPU speed is normally set by resistors.)
" Hello,
The new iBook can be overclocked in software. There are two PLL (clock multipliers). The register HID1 is used to configure them and to switch between them.
I have, with success, changed the clock to 800 MHz. I have installed the CHUD tools from Apple and done the following operations.
1 launch the Reggie application (/Developer/Applications/Reggie)
2. select the HID1 register
3. deselect the bit 15 (if it was yet disabled jump to step 6)
4. click Apply (we select PLL0 as source)
5. select the HID1 register
6. set the bit 24 and clear the bits 25, 26, 27, 28, 29 and 30
7. click Apply (we configure PLL1 to 8x, so 800 MHz)
8. select the HID1 register
9. select the bit 15
10. click Apply (we select PLL1 as source and now we should run to 800 MHz)
Only 800 MHz worked on my ibook. But also, I didn't have the right documentation.
Regards,
Donatello
(I wrote to ask if the speed is reset after a restart (I suspected so)-Mike)
Yes, it resets to 700 MHz. It will be very easy to do a kext that sets the hid1 register during the boot. Currently, I don't have my ibook to try it.
I would like to make a correction.
Step 6, set the bit 24 and clear the bits 25, 26, 27, 28, 29 and 30
[I corrected this in the original remarks above-Mike]
Else I have two remarks:
- the new iBook use a version 1.2 of the 750FX. The fully featured 750FX, able to reach 1GHz, are the 2.0.
- Reggie lets the user enter any value. So it could be dangerous for the iBook because the maximum frequency allowed is 2GHz.
Regards,
Donatello. "
Yesterday's news page had a story with specs/features of the IBM 750FX CPU.
(Note: As with any overclocking, this of course voids the warranty, may not be reliable, etc. etc. - all mods like this are done at your own risk. )
I checked the IBM 750FX specs file linked in yesterday's news and found the following reference. (Some thought the above was a hoax - I don't have an iBook 2002 to try but here's a clip from the 750FX specs)
" (Page 13 under "features" section in power section notes)
"dual PLLs for seamless frequency switching"
(Page 16, para 3.2 Power notes [bold emphasis mine])
"...includes two PLLs allowing the processor clock frequency to be changed "on-the-fly" to match processing requirements.
During reset PLL0 is selected to provide the internal processor (i.e core) clock. The external clock to core clock multiplier is selected using external pins. Thereafter, PLL0 and PLL1 may be controlled using software . The HID1 register contains fields that specify the frequency range of each PLL, the clock multiplier for each PLL, external or internal control of PLL0 and a bit to choose which PLL is selected as the source of the processor clock at any given time."
This sounds like more flexibility than the usual (power saving) clock speed reduction features of many other CPUs.
IBM's G3 750FX CPU Software Overclocking?
(iBook 2002 Owner Report @800MHz) - (*Updated with a correction and more info from the reader*)
About a week ago a reader wrote that the IBM 750FX CPU used in the new 2002 iBooks have a bus/cpu multiplier that can be set via software. (The bus/cpu ratio that determines CPU speed is normally set by resistors.)
" Hello,
The new iBook can be overclocked in software. There are two PLL (clock multipliers). The register HID1 is used to configure them and to switch between them.
I have, with success, changed the clock to 800 MHz. I have installed the CHUD tools from Apple and done the following operations.
1 launch the Reggie application (/Developer/Applications/Reggie)
2. select the HID1 register
3. deselect the bit 15 (if it was yet disabled jump to step 6)
4. click Apply (we select PLL0 as source)
5. select the HID1 register
6. set the bit 24 and clear the bits 25, 26, 27, 28, 29 and 30
7. click Apply (we configure PLL1 to 8x, so 800 MHz)
8. select the HID1 register
9. select the bit 15
10. click Apply (we select PLL1 as source and now we should run to 800 MHz)
Only 800 MHz worked on my ibook. But also, I didn't have the right documentation.
Regards,
Donatello
(I wrote to ask if the speed is reset after a restart (I suspected so)-Mike)
Yes, it resets to 700 MHz. It will be very easy to do a kext that sets the hid1 register during the boot. Currently, I don't have my ibook to try it.
I would like to make a correction.
Step 6, set the bit 24 and clear the bits 25, 26, 27, 28, 29 and 30
[I corrected this in the original remarks above-Mike]
Else I have two remarks:
- the new iBook use a version 1.2 of the 750FX. The fully featured 750FX, able to reach 1GHz, are the 2.0.
- Reggie lets the user enter any value. So it could be dangerous for the iBook because the maximum frequency allowed is 2GHz.
Regards,
Donatello. "
Yesterday's news page had a story with specs/features of the IBM 750FX CPU.
(Note: As with any overclocking, this of course voids the warranty, may not be reliable, etc. etc. - all mods like this are done at your own risk. )
I checked the IBM 750FX specs file linked in yesterday's news and found the following reference. (Some thought the above was a hoax - I don't have an iBook 2002 to try but here's a clip from the 750FX specs)
" (Page 13 under "features" section in power section notes)
"dual PLLs for seamless frequency switching"
(Page 16, para 3.2 Power notes [bold emphasis mine])
"...includes two PLLs allowing the processor clock frequency to be changed "on-the-fly" to match processing requirements.
During reset PLL0 is selected to provide the internal processor (i.e core) clock. The external clock to core clock multiplier is selected using external pins. Thereafter, PLL0 and PLL1 may be controlled using software . The HID1 register contains fields that specify the frequency range of each PLL, the clock multiplier for each PLL, external or internal control of PLL0 and a bit to choose which PLL is selected as the source of the processor clock at any given time."
This sounds like more flexibility than the usual (power saving) clock speed reduction features of many other CPUs.
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