Forge wrote:
I think a detail is being overlooked here.
R200 does not have 3 TMUs per pipe. R200 is 4 pipes, 2 TMUs each. Only R100 (Radeon) and RV200 (Radeon 7500) and their derivatives use the 2*3 pipes/TMUs layout.
Does anyone have any evidence to the contrary?
No. It has 2 TMUs per pipe and 3 pipes. Each pipe can be independently programmed. This gives a total of 6 application usable texture units. Now, there will be a performance hit each time the app goes from 2n to 2n+1 texture units. Look near the bottom of the Radeon 8500's entry on delphi3d for further proof. It lists 'Multitexture Texture Units 6'.
http://www.delphi3d.net/hardware/viewreport.php?report=690
The R100 chips have 3 TMUs per pipe and 2 pipes, but the pipes are not independently programmable. That gives a total of 3 application usable texture units.
The number of pipes has nothing to do with how many textures can be applied per pass, this is simply saying how many pixel the chip is working on at the same time. The R200 has indeed 4 pipes, 2 TMUs, but each TMU can do 2 loopbacks (requires a clock cycle per loopback) so 6 textures can be applied (opengl doesn't really expose physical TMUs, more "logical tmus"). Though I'm wondering if the RV250/280 require different code for more than 3 textures than the 250/280 have only 1 TMU per pipe but can do 5 loopbacks - without specs it's hard to say if there are differences driver-wise. (Slightly off-topic I've also wondered if some driver workarounds for hardware-bugs are still necessary for the RV250.)
Roland
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