Where does the N64 CPU get its clock signal from?

[mr_bigmouth_502]

I'm aware that the n64 can be overclocked by increasing the multiplier from 1.5x to 2x or 3x, but that just got me wondering, can the FSB speed be overclocked instead, and if so, what pin on the CPU can I lift to give it a custom clock signal? It's just a harebrained idea that I came up with in class the other day, and I'm aware that it may have some problems, such as causing the CPU to overheat, or overclocking other components in the N64 that shouldn't be overclocked, such as the RCP, though I'm pretty sure that those problems can be fixed by applying an adequate amount of cooling, and giving the other components a seperate clock signal, respectively. I've never done any sort of console mods before, and I don't completely understand everything there is to understand about N64 modding, though I've read about it before, and though it would be an interesting idea.

This is my first post here, BTW.

[Mario]

The clock is actually part of the chip. There are two pins, and different combinations of attaching them to ground and 3.3v changes the multiplier. There is a guide if you do a quick google search:
http://www.gamesx.com/misctech/n64oc.htm" onclick="window.open(this.href);return false;

Only thing I can say is, I overclocked the N64 in one of my portables to 2.0x and it worked fine. But, after a while (a month or so?) the portable started freezing randomly on startup and needed to be reset a lot of times before it booted correctly. When I undid the overclock it's worked fine since. So, take whatever you want from that. 1.5x overclock might be more stable.

[marshallh]

The CPU clock is supplied by the RCP which is driven with an external PLL

[mr_bigmouth_502]

The CPU clock is supplied by the RCP which is driven with an external PLL

OK, so would it be possible to intercept the signal given from the RCP to the CPU and replace it with a different clock signal? I know that the RCP could have its clock overclocked as well, but that would probably screw things up. BTW, cooling shouldn't be an issue, as this isn't for a portable unit, but rather a plain-old N64 with some aftermarket heatsinks instead of the tiny stock ones.

[marshallh]

The CPU clock is supplied by the RCP which is driven with an external PLL

OK, so would it be possible to intercept the signal given from the RCP to the CPU and replace it with a different clock signal? I know that the RCP could have its clock overclocked as well, but that would probably screw things up. BTW, cooling shouldn't be an issue, as this isn't for a portable unit, but rather a plain-old N64 with some aftermarket heatsinks instead of the tiny stock ones.

why? the only advantage to doing that is having finer granularity compared to the multiplier, if the CPU doesn't run at a higher multipler at stock clock, it doesn't mean it'll run any different with a higher clock

By far the #1 slowdown in all n64 games is fill rate, due to rdram latency and bandwidth requirements especially when using the Z-buffer. You are only going to fix this by clocking the RCP higher, trouble is all games derive timing from vblank (60hz) so increasing this will just make things work like a movie reel being played too fast, and you wouldn't be able to see the generated video signal anyway since the frequencies would now be way out of spec

[mr_bigmouth_502]

The CPU clock is supplied by the RCP which is driven with an external PLL

OK, so would it be possible to intercept the signal given from the RCP to the CPU and replace it with a different clock signal? I know that the RCP could have its clock overclocked as well, but that would probably screw things up. BTW, cooling shouldn't be an issue, as this isn't for a portable unit, but rather a plain-old N64 with some aftermarket heatsinks instead of the tiny stock ones.

why? the only advantage to doing that is having finer granularity compared to the multiplier, if the CPU doesn't run at a higher multipler at stock clock, it doesn't mean it'll run any different with a higher clock

By far the #1 slowdown in all n64 games is fill rate, due to rdram latency and bandwidth requirements especially when using the Z-buffer. You are only going to fix this by clocking the RCP higher, trouble is all games derive timing from vblank (60hz) so increasing this will just make things work like a movie reel being played too fast, and you wouldn't be able to see the generated video signal anyway since the frequencies would now be way out of spec

I was just planning on using this mod for Perfect Dark, and as far as I know, that's one of the few games that actually does benefit from CPU overclocking. I see what you're getting at though, as most other games won't benefit at all from the overclocking. That being said, since Perfect Dark is one of the only games on the N64 that I really play all that much, I think that's a good enough reason for me to try this mod. =P