Based on a educated guess, console development cost. Thanks

[PC-Engine]

It means you first brought up the comparison of the amount customization or lack thereof for the various chips.

But I didn't say one was more custom than the other. Do you have a problem with the definition of similar?

Are you always so angry?

No it's just people like you who can't read are annoying. I think there should be a minimum requirement of a C grade in English 101 for anyone who posts on this board.

 

[archie4oz]

There are instruction differences between the standard SH4, and the variant in the DC - specifically to aid 3D transformation.. not a lot of extra instructions, but enough to make it a 'custom chip' for Sega.

Which ones are they? Are they mysteriously hidden? The only 3D instructions that I'm aware of are FIPR (inner product) and FTRV (vector transform), FRCHG allows fast switching of the FP bit in the FPSCR register, and FSCHG which changes the value of the SZ bit in the FPSCR register to allow FMOV to tranfer paired single-precision floats... And all that is pretty much standard on your off-the-shelf SH-4 (with an FPU that is)...

->The XCPU has the 128 SSE unit (4Floating Point ops/cycle) + the FPU (80 bits) that shares its registers with MMX units... (can be used at the same time FPU/SSE ? I know that's not the case with MMX/FPU since they share registers but what about SSE ?)

Actually there is no "SSE unit + FPU". SSE leverages the FPU execution unit(s) to do packed/vector math. The main difference between it at an implementation like Gekko's or the SH-4 is that SSE has it's own set of registers (XMM) while Gekko and the SH-4 use the FPU registers. Also you don't get 4 fp-ops a cycle on SSE on a P6 core, only 2 (with packed instructions) because the FPU is only 64-bit (well 80-bit actually) and can only compute a half-vector a cycle... Also the reason you don't mix MMX and FPU instructions isn't so much the register usage, it's because with MMX you're doing integer math on FPU registers and it requires an expensive context switch when switching between MMX and FPU instructions...

->And the DC what has ? Can anybody explain me in what consists fp pushing power in the DC ? Please relate to SIMD, FPU units, size and ops.

The DC pretty much has an FPU with 32 32-bit registers divided into two 16 register banks. One bank is addressable as either 16 general single-precision registers, 8 double-precision, or 4 vector register, while the other bank is treated as 8 extended double registers, or a 4x4 matrix. There's no real SIMD instructions other than the packed FMOV instructions, the inner-product and vector transform instructions...

 

[ShinHoshi]

Thanks a lot for the explanation archie.

 

[Ty]

But I didn't say one was more custom than the other. Do you have a problem with the definition of similar?

Right. But you did compare them first (with regard as to how custom they are or how custom they aren't).

In other words, I assumed when you used the phrase, "off-the-shelf" you were referring to how both chips weren't very custom. Logically "custom" is on one end of the spectrum and "off-the-shelf" is on the other end. Capiche?

No it's just people like you who can't read are annoying. I think there should be a minimum requirement of a C grade in English 101 for anyone who posts on this board.

Hey no problems there but you should make sure that you are correct before going off. And even if you don't see that you are wrong here, you were certainly wrong about your comparison of the two per Archie's response.

QED.

 

[PC-Engine]

But I didn't say one was more custom than the other. Do you have a problem with the definition of similar?

Right. But you did compare them first (with regard as to how custom they are or how custom they aren't).

In other words, I assumed when you used the phrase, "off-the-shelf" you were referring to how both chips weren't very custom. Logically "custom" is on one end of the spectrum and "off-the-shelf" is on the other end. Capiche?

No it's just people like you who can't read are annoying. I think there should be a minimum requirement of a C grade in English 101 for anyone who posts on this board.

Hey no problems there but you should make sure that you are correct before going off. And even if you don't see that you are wrong here, you were certainly wrong about your comparison of the two per Archie's response.

QED.

Actually nothing has been definitively proven except that both SH-4 and Gekko is "basically" off-the-shelf with a few custom modifications which if you go back and read my original post, was what I'd already said.