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Power2PC

macrumors newbie
Original poster
Dec 16, 2021
6
5
Hello, This question has likely already been answered many times previously, however curiosity had gotten the best of me to ask on this forum. As likely far fetched as it sounds I'm asking if it is at all possible to change system parameters of the PowerMac G5, such as: Memory Speed, Clock Ratios, BCLK and other parameters as expected through a modifying bootstrap code, firmware or such. Even if this ends up not being practical or possible, I would appreciate knowing more about the inner working of the G5's architecture.
For me, I'm not extremely knowledged on the full system architecture of the Power Mac G5 (The PCI-e Models to be more exact as that's what I have) and how the various devices communicate with one another (However most I can make educated guesses to how they interface with the system from studying regular motherboards). For the basics I can gather that the Host G5 processor communicates at exactly half the operating clock of its primary clock speed (E.g. 2.3Ghz CPU = 1.15Ghz FSB), and that (from studying the traces and general placement, along with online research) the memory controller is embedded in the system chipset or "U3" / "U4" as called through software. As someone who is modestly knowledgeable in the workings of computers, If anybody knows more about the PowerMac G5 system architecture and could explain then it would be much appreciated.
This post may (and probably will) just be a waste of time and the system parameters may just be automatically calculated or fixed in hardware and non re-programmable, but I'd appreciate the insight regardless. Thank you to anyone in advance.
 

eyoungren

macrumors Penryn
Aug 31, 2011
29,603
28,365
If what you want to do is in any way possible (and I do not know/believe it is) then you probably want to start looking into Open Firmware.

It's possible to spoof a different processor speed to install Leopard on an unsupported G4 and that's done using OF, so that's the only reason I would even think this might be possible here.

@LightBulbFun would probably know way better than I.
 
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Power2PC

macrumors newbie
Original poster
Dec 16, 2021
6
5
If what you want to do is in any way possible (and I do not know/believe it is) then you probably want to start looking into Open Firmware.

It's possible to spoof a different processor speed to install Leopard on an unsupported G4 and that's done using OF, so that's the only reason I would even think this might be possible here.

@LightBulbFun would probably know way better than I.

New development. After scouring the IBM DataSheet on the PPC970MP CPU series I managed to find information that the CPU multiplier, BUS multiplier and ratios for the CPU specifically can be modified. The DataSheet pages: 43, 52, 53 linked: (http://datasheets.chipdb.org/IBM/PowerPC/970/PowerPC-970MP.pdf#page52). From what I read, I can only assume with more research on the chipset that the rest of the system parameters can be altered, including system memory parameters and BLCK. (however those will likely be a little more difficult to work out). If anyone knows the DataSheet or part number of the chipset used in the PCIE PowerMac G5 please let me know asap.
 

barracuda156

macrumors 68020
Sep 3, 2021
2,295
1,514
Hello, This question has likely already been answered many times previously, however curiosity had gotten the best of me to ask on this forum. As likely far fetched as it sounds I'm asking if it is at all possible to change system parameters of the PowerMac G5, such as: Memory Speed, Clock Ratios, BCLK and other parameters as expected through a modifying bootstrap code, firmware or such. Even if this ends up not being practical or possible, I would appreciate knowing more about the inner working of the G5's architecture.

Just curious, what would you possibly need that for?
 

Power2PC

macrumors newbie
Original poster
Dec 16, 2021
6
5
Just curious, what would you possibly need that for?
Hi, this is part of a project I have been working on to document the system capabilities and the architecture of the late 05 G5 systems. I was curious about knowing more on the system hardware within. As of now If you happened to know any details about the main system chipset or “U4” memory controller (part numbers, datasets ect), then I would be most grateful. Best regards- Power2PC
 
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Power2PC

macrumors newbie
Original poster
Dec 16, 2021
6
5
Overclocking. :)
Hello, this forum is not about the topic of overclocking specifically, feel free to discuss as you wish as I have nothing against discouraging curiosities for the interest of others. This thread is mainly about discussing the system architecture and associated parameters for technical documentation of G5 late 05 systems.
 

joevt

macrumors 604
Jun 21, 2012
6,932
4,233
I suppose some of what you seek may be in the Forth code, but maybe some stuff is not.

I have dumps of compiled FCode from a Quad G5 at https://forums.macrumors.com/thread...at-useful-for-something.2318099/post-30480524
The compiled FCode is from a memory dump - not from the ROM. While I can get the ROM from a Quad G5 - it's compressed or something. It would be nice to know how to uncompress it to get the FCode tokens which can be converted to Forth more easily. Alternatively, it would be nice to write a version of the see command to work with the compiled FCode output (and it can be made smarter to handle the different branch/loop tokens better).
 

barracuda156

macrumors 68020
Sep 3, 2021
2,295
1,514
Hi, this is part of a project I have been working on to document the system capabilities and the architecture of the late 05 G5 systems. I was curious about knowing more on the system hardware within. As of now If you happened to know any details about the main system chipset or “U4” memory controller (part numbers, datasets ect), then I would be most grateful. Best regards- Power2PC

Unfortunately, I know very little of hardware internals. Perhaps that could be a useful knowledge, but as everywhere, we face trade-offs in terms of allocation of time. Now I am struggling with compilation on G5 – the big aim is to make gcc11 build :)
 

PowerfulEra

macrumors member
Jul 20, 2017
97
49
Is it even possible to overclock the G5 Quad to at least 3.0 ???
Who knows. 3.0 would be sick but would need custom water cooling setup like he is working on. If my take on his idea will be implemented there will need to be modifications done because of copper 240mm radiator.
 
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