console CPUs questions

Anarchist420

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Feb 13, 2010
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Is it true that the N64's CPU was on a 350 nm process and that the Saturn's SH2s were done on a 250 nm process?

I had thought I read that was the case. However, that doesn't make sense due to the fact that the N64's CPU had an FPU, had much more cache, and was clocked faster than the SH2s in the Saturn. Does an SH2 have any advantages over the MIPS 4000 series-derivative used by the N64?

Also, I heard some N64 games didn't use a Z-buffer. Did games use the CPU for depth testing if they didn't use the RDP's Z-buffer? I thought I heard that Factor5 didn't use the Z-buffer for Indiana Jones and the Infernal Machine, which would make sense due to the fact that the N64 only had a 16 bit zbuffer (which is very low precision).

What is/are likely reason/s didn't Nintendo go with a 250 nm process (assuming they used a 350 nm process)? Did have to do with transistor density or was it due to something else?
 

Arzachel

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Apr 7, 2011
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Is it true that the N64's CPU was on a 350 nm process and that the Saturn's SH2s were done on a 250 nm process?

I had thought I read that was the case. However, that doesn't make sense due to the fact that the N64's CPU had an FPU, had much more cache, and was clocked faster than the SH2s in the Saturn. Does an SH2 have any advantages over the MIPS 4000 series-derivative used by the N64?

Also, I heard some N64 games didn't use a Z-buffer. Did games use the CPU for depth testing if they didn't use the RDP's Z-buffer? I thought I heard that Factor5 didn't use the Z-buffer for Indiana Jones and the Infernal Machine, which would make sense due to the fact that the N64 only had a 16 bit zbuffer (which is very low precision).

What is/are likely reason/s didn't Nintendo go with a 250 nm process (assuming they used a 350 nm process)? Did have to do with transistor density or was it due to something else?

http://www.ehow.com/info_7819305_specs-hitachi-sh2-processors.html

According to this, the SH2 is only 5.45mm² large and manufactured on a 0.8 micron process. On the n64, probably the same reasons were true then as are now, cost and supply.
 

Ferzerp

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Oct 12, 1999
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Nintendo is typically all about cost. They consistently have the cheapest console on the market.

I'm pretty sure it's been this way since the NES, but that's 25 years of memory, so I may be incorrect.
 

Cerb

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Aug 26, 2000
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Is it true that the N64's CPU was on a 350 nm process and that the Saturn's SH2s were done on a 250 nm process?

I had thought I read that was the case. However, that doesn't make sense due to the fact that the N64's CPU had an FPU, had much more cache, and was clocked faster than the SH2s in the Saturn. Does an SH2 have any advantages over the MIPS 4000 series-derivative used by the N64?
Code size, faster when working on small pieces of data, and business (while not strictly produced for Sega, Sega's needs influenced SH development). Nintendo's MIPS was much more powerful, and had shared speedy RAM. 486/Pentium int, and with far faster scalar and vector FP.

Also, I heard some N64 games didn't use a Z-buffer. Did games use the CPU for depth testing if they didn't use the RDP's Z-buffer? I thought I heard that Factor5 didn't use the Z-buffer for Indiana Jones and the Infernal Machine, which would make sense due to the fact that the N64 only had a 16 bit zbuffer (which is very low precision).
I don't know about using a RCP Z-buffer, but if it was difficult to use, or didn't perform well enough, it's not like they lacked the computational power on the main CPU. I doubt the precision was too little (16-bit storage does not mean 16-bit processing). It's not like the scene complexity was high on N64 games.
 

Exophase

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Apr 19, 2012
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There is no way Saturn's SH2s were manufactured on a 250nm process. I think you're confusing them with the SH4 in Dreamcast, which was publicized as being on 250nm. The first 250nm product I could find reference of was a Pentium MMX shrink from Intel in 1997, and I really don't think Hitachi (or whoever fabbed the chips) beat Intel to this process by 3+ years. If it introduced in 1993 at 800nm then I'm sure that's what was in Saturn since that wasn't that long afterwards. Likewise I doubt Nintendo had access to something better than 350nm, which was cutting edge when N64 was being developed. N64 was supposed to be out earlier than it was, in 1995 IIRC.

You can't use software depth buffering with a hardware GPU, or at least not in the strict sense. What you can do is replace depth buffering with depth sorting, where the polygons are sorted ahead of time. This could have been done partially or entirely on the RSP instead of the CPU.

And I can see why it was beneficial to do this. Z-buffering cost you a lot of fill rate. Pixels would usually just cost a write on the bus, and the games probably typically used 16bpp color formats. Depth buffering would always cost a load and a store, and games used 16bit depth buffers. So the usual bandwidth needs may have increased triple-fold, which I'm sure had a direct impact on fill rate even with the relatively high bandwidth RDRAM. The GPU itself probably needed extra clocks for depth buffering too.

That's only one half of the problem though. The other issue is that on N64 the RDP didn't perform any triangle setup, so it had to be done on the RSP (or CPU). This involves calculating slopes for all of the parameters you're interpolating. Depth would usually need more good bits than color, which would result in more RSP operations (since its native vector width wasn't 32-bit per element). And that would mean transferring more data to the RDP, which would take more clock cycles over its FIFO. So in the long run I think enabling depth buffering had a big impact on your triangle rate as well as your fill rate.

If you're performing depth sorting there's probably a lot you can do to design your game so that you don't have to sort at a per-triangle granularity. For instance, whole meshes may follow orderings that are angle independent. This is probably even more true if the camera is limited in some way.
 
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sm625

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May 6, 2011
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Nintendo is typically all about cost. They consistently have the cheapest console on the market.

I'm pretty sure it's been this way since the NES, but that's 25 years of memory, so I may be incorrect.

SNES was more complex and had a higher build cost than the Sega Genesis. Same goes for the N64 vs the original playstation. If you took the cd drive out of the playstation, its bill of materials would have been much lower.
 

Anarchist420

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Thanks for the info everyone:) It boggled my mind when I read in a Gamepro that the saturn used a 250 nm process, given that they had to use two of them clocked rather slow with very little on die cache.

The N64 sounds like it may have been just as much of a b**** to program for as the Sega Saturn since the N64's GPU was limited.