Overclocking GameCube CPU and GPU?

[CosmoCortney]

Hello,
i'm new here and i hope i can get any help here...
the title of this topic already explains what i would like to know.
probably a few guys of you are thinking it's nonsense to overclock the GC.
But i do a lot of RAM hacking on this console (hacking AR and Gecko codes) and to be able to accelerate or slow down the CPU would be helpful in some cases.
it also could be interesting to overclock the GPU too.
also, someone knows something about overclocking the cube?
thanks

[liquitt]

we had this topic a few times on irc ... the problem is, it's super stressy to get to the important part of the CPU - which is right under it.
so you would have to desolder the cpu....

[emu_kidid]

You could do as liquitt mentioned but the multiplier unlock pin or whatever it was is going to GND and there is no trace we can cut. You'd have to remove the CPU, isolate the pin somehow and have it come out from under the CPU and go to the desired voltage to unlock it - so yeah, probably not going to happen unless if you somehow socketed the chip. IMHO - WAY too much effort.

[Cubdax]

I found this pic.



What could be the multiplier unlock pin?

[Diminuendo]

So what are the advantages? I think the obvious thing is removing choppy framerates in Tales of Symphonia and Giest

I remember a topic about two months ago in that mentioned the GameCube could output 1080p, but I think that with a stock CPU it wouldn't be anywhere near playable. I'm going to ask you Emu_Kidd, you basically know Gamecube inside and out, what do you think clock multiplier would need to be at to achieve this at 30fps?

All this stuff might not be feasible or worthwhile for everyone to do but I personally would love to see it happen at least once. I'll gladly donate a gamecube to make it happen.

[emu_kidid]

Cubdax, if you look at the datasheet PDF you can find that info, I don't recall off hand.

Diminuendo, you can never get 1080p, there's a limit to the hardware below that. It'd 100% be for homebrew purposes, but it's not worth the effort.

[Diminuendo]

Ok, do you think with an overclock we could increase the resolution even a little?

[emu_kidid]

No.

[Cubdax]

emu_kidid, I look at the datasheet PDF and the only info I have found is:

Bus interface features include the following
– Selectable bus-to-core clock frequency ratios of 2x, 2.5x, 3x, 3.5x, 4x, 4.5x ... 8x and 10x. (2x to 8x, all half-clock multipliers in-between)
– A 64-bit, split-transaction external data bus with burst transfers
– Support for address pipelining and limited out-of-order bus transactions
– Single-entry load queue
– Single-entry instruction fetch queue
– Two-entry L1 cache castout queue
– No-DRTRY mode eliminates the DRTRY signal from the qualified bus grant. This allows the forwarding of data during load operations to the internal core one bus cycle sooner than if the use of DRTRY is enabled.

and

1.2.9 Clocking
Gekko requires a single system clock input, SYSCLK, that represents the bus interface frequency. Internally, the processor uses a phase-locked loop (PLL) circuit to generate a master core clock that is frequency-multiplied and phase-locked to the SYSCLK input. This core frequency is used to operate the internal circuitry.
The PLL is configured by the PLL_CFG[0–3] signals, which select the multiplier that the PLL uses to multiply the SYSCLK frequency up to the internal core frequency. The feedback in the PLL guarantees that the processor clock is phase locked to the bus clock, regardless of process variations, temperature changes, or parasitic capacitances.
The PLL also ensures a 50% duty cycle for the processor clock.
Gekko supports various processor-to-bus clock frequency ratios, although not all ratios are available for all frequencies. Configuration of the processor/bus clock ratios is displayed through a Gekko-specific register, HID1. For information about supported clock frequencies, see the Gekko hardware specifications.

what can we do with this information?

[emu_kidid]

haven't been able to modify HID1, unless if we need to reset the PPC or something. I guess it needs a revisit.

[tueidj]

HID1 is read-only, it just tells the state of the PLL_CFG signals (which are physical pins on the CPU).

[emu_kidid]

hopes crushed, is our only hope to physically change the state from the pin?

[tueidj]

Unless instead of the multiplier you change the system clock somehow, but then everything else (RAM, GPU etc.) would be overclocked as well. There's nothing to gain anyway as shown by the wii.