720p 64bit framebuffer size? Educated guesses here please

[Titanio]

Okay, FSAA as SSAA...

Backbuffer bandwidth = 42 MB x 60 FPS x (2 read|write x 5 overdraw)* ~ 24.6 Gbytes/sec

* Squeak, does your definition of overdraw take into account read|writes? If not, then this would be halved to 12.3 GBytes/sec...

I understand this is a worst case scenario but doesn't that make the PS3 CPU bandwidth somewhat limited?

All this Back-buffer stuff it needs to travel on the main CPU bus right? not the Bus to the Ram on the GPU? And the main CPU bus only has about 25gb/s of bandwidth.

So, if it's ballpark 12.3GB/s for the backbuffer bandwidth, doesn't that leave the main bus with only around 13gb/s available?

Or does all this backbuffer data travel to the GPU memory leaving the CPU bus free for everything else?

The backbuffer/frontbuffer can go wherever you like. Not sure where you got the idea it could only go to XDR?

 

[scooby_dooby]

I thought it had to goto the CPU to be processed but I guess not...

 

[Titanio]

I thought it had to goto the CPU to be processed but I guess not...

You can send data to the CPU for processing, but it's totally optional. In that case, also, you may be able to send the frame in chunks to SPE's local memory directly, without touching XDR (though I'm still hazy on the latter part..The SPEs can snoop data coming from FlexIO off the EIB, but I'm not sure if the data is taken off the EIB at that point, and thus prevented from heading to XDR, or if the data has to continue on to XDR).

 

[scooby_dooby]

I thought it had to goto the CPU to be processed but I guess not...

You can send data to the CPU for processing, but it's totally optional. In that case, also, you may be able to send the frame in chunks to SPE's local memory directly, without touching XDR (though I'm still hazy on the latter part..The SPEs can snoop data coming from FlexIO off the EIB, but I'm not sure if the data is taken off the EIB at that point, and thus prevented from heading to XDR, or if the data has to continue on to XDR).

I read in one of the CELL documents that direct communication to the SPE's, althugh possible, was highly discouraged, and that all processing requests should go through the main PPE.