On Mar 6, 2012, at 11:01 PM, Wayne Stewart wrote:
I've been trying to do something with a MDD that was a little beyond
it so I overclocked a 1.42 to 1.5ghz. That wasn't quite enough so I
tried for 1.58ghz.
System Profiler is saying 1.5ghz. Xbench tests seems to be showing the
correct amount of speedup though it's also saying I have 1.5ghz
processors.
I'm wondering if I might have had one bad resistor and am running one
processor at 1.58 and one at 1.5ghz. I guess the reason I'm wondering
is that years ago I tried OCing for the first time with a dual 867 and
only did one set of resistors. It felt faster but I had each
processor running at a different speed and System Profiler was still
saying 867. When I did the second set it read the faster speed.
I overclocked my 1.42GHz Mini to 1.58GHz. The problem with System
Profiler & About This Mac is that they don't actually measure the CPU
speed. The firmware has values built-in, and it's a simple look-up
process of stored possible values. The problem with 1.58GHz is that
Apple never made any Mac with 1.58GHz CPU speed, so that value isn't
stored in the look-up table. On the Mini, instead of reading 1.5GHz,
which is a possible value, for some reason it would say 750MHz.
The solution was to patch the firmware using a one-time mod by booting
into Open Firmware and patching the values in the look-up table so
that 1.58GHz now corresponds to whatever CPU/Bus parameter is being
measured. This patch won't persist thru a PRAM zap or NVRAM reset, and
if your PRAM battery dies you'd need to do the patch again.
Here's the patch I used for my G4 Mini. It may or may not work for
your MDD? There's no danger AFAIK, if you need to get back to the OEM
firmware just zap the PRAM or reset the NVRAM and all is back to
normal. This should also fix the L2 cache size if it's reported
incorrectly:
These are the values for 1.58GHz overclock:
1.58 GHz PowerPC G4
5e2ce2fd = 1579999997 = " clock frequency"
5e1da0c0 = 1579000000 = " rounded-clock-frequency"
5e178682 = 1578600066 = " recalced-clock-frequency"
Here's the instructions on how to persist the 1.58GHz into the system
so that "About This Mac" works properly:
1. Reboot the computer holding down Cmd-Opt-O-F to enter the Open
Firmware command line.
2. Type nvedit and press Return
3. Enter the following script exactly, pressing Return at the end of
each line.
dev /
9eb18ef encode-int " clock-frequency" property
dev /cpus
dev PowerPC,G4@0
5e2ce2fd encode-int " clock-frequency" property
9eb18ef encode-int " bus-frequency" property
5e1da0c0 encode-int " rounded-clock-frequency" property
5e178682 encode-int " recalced-clock-frequency" property
27ac63b encode-int " timebase-frequency" property
dev l2-cache
5e2ce2fd encode-int " clock-frequency" property
dev /
4. Press Ctrl-C to exit the editor.
5. Type nvstore and press Return
6. Type setenv use-nvramrc? true and then press Return
7. Type reset-all and press Return
If you use these instructions please report back the results so we'll
know whether or not they work on the MDD also.
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