AMD have their fingers in many pies recently, pushing PC development along with providing the APU technology residing inside the PS4 and X1. Recently, AMD’s own Developers Guide for the BIOS and Kernels of the Kevari hints of remnants of GDDR5 support that isn’t present in the finished desktop product.
The guide references four DRAM controllers (labelled as DCT0 through to DCT3). But in the finished product we currently have two of these memory controllers disabled. This leaves Kevari with DCT0 and DCT3 functional, DCT1 and DCT2 aren’t functional. This means that at one time or another, there had been plans for the Kevari architecture to support not only four memory controllers, thus much higher memory bandwidth. Crucially, GDDR5 support missing, but is reference in the document.
“The DRAM controller and the phy are configured for GDDR5 mode. Note: this mode may not be supported by this processor. See section 2.9, or consult processor data sheet to determine which modes are supported.”
Click for larger – Notice how it says “GDDR5 memory isn’t supported”
The issue facing Kevari, especially as a higher performance part (which lots of Shaders) is lack of memory bandwidth to feed them. DDR3 memory, which is present on most desktops just isn’t capable. Typically, PC’s have a discrete GPU which contains several GB of high speed GDDR5 along with a wide bus, providing 200GB/s+ bandwidth.
Kevari pushes towards GPGPU (or AMD’s Fusion as they prefer to call it), the idea of leveraging the GPU’s massive parallel processing to help the CPU process certain tasks. The CPU tells the GPU what to do, sharing the same memory address space (Unified Memory Address). If AMD want to push the sort of graphical processing power which the next generation consoles (Sony’s Playstation 4 and Microsoft’s Xbox One) are using then we’ll need more bandwidth. One way to do that would be GDDR5 RAM.
Another option would be similar to the Xbox One, or Intel’s Haswell design. With Haswell, Intel bolted on 128MB of high speed memory for graphics (eDRAM). Microsoft’s Xbox One SoC (System on Chip) meanwhile contains 12 CU (compute Units, 64 shaders per CU). 32MB of eSRAM provides the high speed memory bandwidth the GPU hungers for.
It’s possible for AMD to easily make a great APU option, particularly for Valve’s Steam Machines. High speed DDR3, using a similar bus setup as the Xbox One (which is 256-Bit, providing around 68GB/s) and a good chunk of on board high speed RAM, either embedded or as a daughter die. 12 Compute Units (768 Shaders) would provide the same kind of grunt as the Xbox One. It’d be pretty easy in theory for AMD to ramp this up to 20 CU’s, which would be more power than PS4.
It’s clear that AMD could easily change things up for Kevari (or its successor) and we could have a lot of easy compute power. Combine that with PCIE 3 (or PCIE 4 if it’s standard by then) and CrossFire with a discrete GPU could lead to some interesting options for gamers.
Thanks to Beyond3d
