Question about eDRAM related Issue

[Strange]

After reading various articles, I think (or at least I hope) I have a fairly good idea about what the eDRAM actually does for the Xenos.

From my knowledge, "basically" it is used for reducing the Xenos bandwidth usage on the RAM that the CPU also has to use taking away the bandwidth of the frame buffer. I hope I didn't get that wrong.

However, after scanning through numerous threads, I havn't been able to spot a ballpark figure of how much of the 22.4GB/s going to the RAM is freed by the eDRAM and exactly how much of the 256GB/S is actually utilized (I suppose these two figures may actually differ due to tiling?).
I would imagine that this figure depends on both the resolution and the level of AA.

I hope answering this question wouldn't require anyone to break their NDAs.

Thanks to anyone who responds, your help is appreciated. :smile:


PS: I hope my first post doesn't break any Forum rules, as that will suck for me

 

[Shifty Geezer]

However, after scanning through numerous threads, I havn't been able to spot a ballpark figure of how much of the 22.4GB/s going to the RAM is freed by the eDRAM and exactly how much of the 256GB/S is actually utilized.

The eDRAM saves 256 GB/s from the main RAM, and 256 GB/s is actually utilized - but in spits and spurts. It's enough bandwidth that the functions of the logic in the eDRAM are never stalled, but they're not using this bandwidth 24/7.

As I understand it anyway, but I'm far from an expert!

 

[Shezad]

Is not possible to understand how much banwidth the EDRAM saves from the main ram because is a value dependent on many variables (number of pixels, resolution, frames).
What you can say is that with this huge number you can carry on very expensive operations on pixels like alpha blending, particle and AA.

 

[Shifty Geezer]

Is not possible to understand how much banwidth the EDRAM saves from the main ram because is a value dependent on many variables (number of pixels, resolution, frames).

As I said, it's 256 GB/s saved, because when the logic is running full tilt, that's how quickly it gets through data. Now that could be 256 GB/s for only 10 MB of data per frame, at 30 fps being 300 MB/s BW used...but that's measuring different things.

 

[AlNom]

So with the eDRAM taking care of all that, how much of the 22GB/s is potentially used? Enough bandwidth left for CPU <-> RAM

 

[Shifty Geezer]

The RAM BW is used for graphics data - textures, models, and different buffers. It's shared with the CPU, so if the CPU is munching 10 GB/s for the game (AI, physics, yadayada), you've got 12 GB/s left for graphics data.

 

[AlNom]

The RAM BW is used for graphics data - textures, models, and different buffers. It's shared with the CPU, so if the CPU is munching 10 GB/s for the game (AI, physics, yadayada), you've got 12 GB/s left for graphics data.

Ah ok. Wasn't sure what made up the graphics data versus the eDRAM. I should have deduced that.