Question regarding R520 and R580

[Jawed]

R520 has four quads. Each quad has:

• four texture pipes,
• four shader pipes and
• four ROP pipes.

R580 also has four quads. Each quad has:

• four texture pipes,
• 12 shader pipes and
• four ROP pipes.

The shader pipes in both R520 and R580 consist of a primary ALU that can execute all maths instructions and a secondary ALU with minimal functionality.

R580's 12 shader pipes in each quad take it in turns to use the texture and ROP pipes in the quad - four pipes at a time.

Jawed

 

[Radeon600]

R580 will have three Shader Units in single group of Quad. But I don't think it will be more than two Quads, which equals 24 'Independent' Shader Units.

So, if it has 4 group of Quads, then it literally means 48 Shader Units with both 'FULL' ALUs, so, I don't think it will be of 96 Shader Units as what ATI itself call it?

In my opinion, there will be two Quads with 48 Shader ALUs (Vec3+Scalar)

 

[Radeon600]

Or it could be that Nvidia's 7800GTX second Shader ALU isn't as powerfull than one, even if second could do MADD operations?

 

[Jawed]

Both of the 7800 ALUs are fully functional for all maths ops.

One of these two ALUs is also used to perform texture address calculations. Which means that sometimes it's not available for general shader maths instructions.

ATI GPUs have a dedicated ALU for texture address calculations.

Jawed

 

[Radeon600]

One of these two ALUs is also used to perform texture address calculations. Which means that sometimes it's not available for general shader maths instructions.
Jawed

I think you are talking about Texture Unit?
http://img.neoseeker.com/v_image.php?articleid=1807&image=19

But, I am still wondering whether R580 has 24 (2 Quads) Shader with DOT ALUs or 48 (4 Quads) with Mini or DOT?

 

[Jawed]

No. The texture unit can only work with an address calculated for it. Which is done by the first ALU in NVidia GPUs and by a dedicated ALU in ATI GPUs.

Jawed

 

[Radeon600]

Ok.

But what you think about the Quads in R580?


Thanks for your time though.

 

[Kaotik]

Ok.

But what you think about the Quads in R580?


Thanks for your time though.

at least I believe it will be 4x 12 shader unit "Shader Cores" like R520 is 4x 4 shader unit "Shader Cores", instead of 12x 4 shader unit "Shader Cores"

 

[Radeon600]

You mean to say 2 Quads or 4 Quads?

 

[Radeon600]

Also, it will have 16 back end outputs. So 2 Quads looks quite resonable to me.

 

[Kaotik]

You mean to say 2 Quads or 4 Quads?

2 quads?
The way I see it is that it will have 16 ROP's, 16 Texture units and 4 Shader Cores, which all have 12 shader units.
I don't see how you can even try to fit "2 Quads" to that scheme

 

[Radeon600]

Ok, I agree with you for a while, but does it means that each Shader ALU is capable of DOT operations, making it to almost 96 Shader Units?, just like R520, ATI says it has 16 Shader Units with 2 ALU, but one ALU isn't capable of doing MADD.

 

[Kaotik]

Ok, I agree with you for a while, but does it means that each Shader ALU is capable of DOT operations, making it to almost 96 Shader Units?, just like R520, ATI says it has 16 Shader Units with 2 ALU, but one ALU isn't capable of doing MADD.

No, it will have 48 Shader Units similar to those 16 of R520

 

[Radeon600]

4 Quads, two Single Shader ALU per Shader Unit with DOT and other with Normal.


Well, lets see...although thanks everyone for their valuable input.

 

[Radeon600]

I don't see how you can even try to fit "2 Quads" to that scheme

Well, I think that if both Shader ALUs are capable of doing MADD operations, then each pipeline is already dividing itself into two, hence making it into 48 Pixel Pipelines (Total 96 Shader Unit, but other Shader ALU is not effective). And since, ATI also seems to follow this (as like R520) so I think, R580 might come up with 2 Quads or 4 Quads. But most probaly as you said before that it will be like R520, so I think it could be right, that it might have actually 96 Shader Unit, but 1 Shader Unit is not as capable as the other one, so making it total of 48 Shader Units, hence 1:3 ratio.

 

[Radeon600]

but 1 Shader Unit is not as capable as the other one, so making it total of 48 Shader Units, hence 1:3 ratio.

I mean to say, but 1 Shader ALU is not as capable as the other one.

 

[Kaotik]

Well, I think that if both Shader ALUs are capable of doing MADD operations, then each pipeline is already dividing itself into two, hence making it into 48 Pixel Pipelines (Total 96 Shader Unit, but other Shader ALU is not effective). And since, ATI also seems to follow this (as like R520) so I think, R580 might come up with 2 Quads or 4 Quads. But most probaly as you said before that it will be like R520, so I think it could be right, that it might have actually 96 Shader Unit, but 1 Shader Unit is not as capable as the other one, so making it total of 48 Shader Units, hence 1:3 ratio.

You seem to mix ALU & what ATI calls "Shader Unit" to mean the same, which they're not.

 

[Radeon600]

You seem to mix ALU & what ATI calls "Shader Unit" to mean the same, which they're not.

Ok, well doesn't R520 has 32 Shader Units, in which 16 are not as usefull?

 

[Kaotik]

Ok, well doesn't R520 has 32 Shader Units, in which 16 are not as usefull?

No it has 16 Shader Units

This is what ATI calls one shader unit:

• ALU 1
  • 1 Vec3 ADD + Input Modifier
  • 1 Scalar ADD + Input Modifier
• ALU 2
  • 1 Vec3 ADD/MULL/MADD
  • 1 Scalar ADD/MULL/MADD
• Branch Execution Unit
  • 1 Flow Control Instruction

 

[Radeon600]

Well, I am not too sure at the moment.

But in above clarrification, it seems there is only one Shader ALU which is doing most of the work because it is capable of doing MADD Operations. While, second Shader ALU has ADD only. Its more like 'Mini ALU' to me.


Thanks again.