R350 and RV350 don't offer same functionality?

[Zvekan]

I was just browsing ATI's products pages and noticed a small difference between Radeon 9800 and Radeon 9600.

Here is what they say for 9800:

SMARTSHADERâ„¢ 2.1
Full support for Microsoft® DirectX® 9.0 programmable vertex and pixel shaders in hardware
2.0 Vertex Shaders support vertex programs up to 65,280 instructions with flow control
2.0 Pixel Shaders support up to 16 textures per rendering pass
New F-buffer technology supports pixel shader programs with unlimited instructions
128-bit, 64-bit & 32-bit per pixel floating point color formats
Multiple Render Target (MRT) support
Shadow volume rendering acceleration
Complete feature set also supported in OpenGL® via extensions

And this is Radeon 9600:

SMARTSHADERâ„¢ 2.0
Programmable pixel and vertex shaders
16 textures per pass
Pixel shaders up to 160 instructions with 128-bit floating point precision
Vertex shaders up to 1024 instructions with flow control
Multiple render target support
Shadow volume rendering acceleration
High precision 10-bit per channel frame buffer support
Supports DirectX® 9.0 and the latest version of OpenGL®


So it is possible that some complicated vertex shaders (that are very unlikely to be found in todays games) won't function on RV350 based cards?

Until now I was under impression that RV350 is based on R350 design (F-buffer and SS 2.1), but it appears that it is based on R300 and therfore doesn't offer full functionality of it's stronger breathen.

Zvekan

 

[Dave Baumann]

No the VS is the same, its just a difference in how they are quoted (one with loops and subroutines and one without). Where they differ mainly is the fact that R350 has the F-Buffer support and RV350 doesn't

 

[Zvekan]

So what are the numbers then?

1024 without loopback seems a bit too much, as I think they used that number to show that NV30 is supposedly better offering VS 2.0+ functionality.

65280 is number with loopbacks? It appears also to high, while using F-Buffer practicly raises limit to indefinetly (but uses more clocks).

Also is F-Buffer currently exposed via drivers and what are practical differences betwen SS 2.0 and SS 2.1 apart F-Buffer?



Thnx,

Zvekan

 

[GraphixViolence]

I remember hearing somewhere that the original VS 2.0 spec limited the loop counter to 4, but this was later increased to 256. At some point ATI changed the instruction count numbers in their product specs from 1024 to 65,280. Since the R300 was announced well before DX9 was available, this may well have been the case.

AFAIK the F-buffer is only useful for pixel shaders, not vertex shaders, and is not yet exposed in ATI's drivers. I don't think there are any other differences between SS 2.0 and SS 2.1. The 1024 instruction figure in the 9600 specs is probably just a typo.

 

[rwolf]

I would expect the 9600 to behave the same as a 9700 not the 9800.