AMD Kaveri Docs Reference Quad-Channel Memory Interface, GDDR5 Option
by Anand Lal Shimpi on January 16, 2014 10:51 PM EST
Our own Ryan Smith pointed me at an excellent thread on Beyond3D where forum member yuri ran across a reference to additional memory controllers in AMD's recently released Kaveri APU. AMD's latest BIOS and Kernel Developer's Guide (BKDG 3.00) for Kaveri includes a reference to four DRAM controllers (DCT0 - 3) with only two in use (DCT0 and DCT3). The same guide also references a Gddr5Mode option for each DRAM controller.
Let me be very clear here: there's no chance that the recently launched Kaveri will be capable of GDDR5 or 4 x 64-bit memory operation (Socket-FM2+ pin-out alone would be an obvious limitation), but it's very possible that there were plans for one (or both) of those things in an AMD APU. Memory bandwidth can be a huge limit to scaling processor graphics performance, especially since the GPU has to share its limited bandwidth to main memory with a handful of CPU cores. Intel's workaround with Haswell was to pair it with 128MB of on-package eDRAM. AMD has typically shied away from more exotic solutions, leaving the launched Kaveri looking pretty normal on the memory bandwidth front.
In our Kaveri review, we asked the question whether or not any of you would be interested in a big Kaveri option with 12 - 20 CUs (768 - 1280 SPs) enabled, basically a high-end variant of the Xbox One or PS4 SoC. AMD would need a substantial increase in memory bandwidth to make such a thing feasible, but based on AMD's own docs it looks like that may not be too difficult to get.
There were rumors a while back of Kaveri using GDDR5 on a stick but it looks like nothing ever came of that. The options for a higher end Kaveri APU would have to be:
1) 256-bit wide DDR3 interface with standard DIMM slots, or
2) 256-bit wide GDDR5 interface with memory soldered down on the motherboard
I do wonder if AMD would consider the first option and tossing some high-speed memory on-die (similar to the Xbox One SoC).
All of this is an interesting academic exercise though, which brings me back to our original question from the Kaveri review. If you had the building blocks AMD has (Steamroller cores and GCN CUs) and the potential for a wider memory interface, would you try building a high-end APU for the desktop? If so, what would you build and why?
I know I'd be interested in a 2-module Steamroller core + 20 CUs with a 256-bit wide DDR3 interface, assuming AMD could stick some high-bandwidth memory on-die as well. More or less a high-end version of the Xbox One SoC. Such a thing would interest me but I'm not sure if anyone would buy it. Leave your thoughts in the comments below, I'm sure some important folks will get to read them :)
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smartypnt4 - Thursday, January 16, 2014 - link
I'm going to have to agree with Anand here: such a thing would indeed interest me greatly. I'd love to be able to have a machine like that just to poke around on. That said, I'm not sure if it would merit a purchase at this point or not. It would make an incredible Steam machine or HTPC, but I don't currently have a need for it since my main desktop is close enough to my home theater to use a 50' HDMI cable to hook it up (small apartments are so fun).I suppose something like this would tempt me greatly if I was in the situation where I couldn't have my current setup. I would want a 4-module Steamroller core, though. Other than that, putting this in something like the Gigabyte Brix or NUC box for a HTPC or Steam box would be quite awesome indeed, especially with Mantle support (if that pans out like AMD says it will). Then again, the sales of such a chip would be tied directly to the success of SteamOS as well, sooo...
That was a lot of rambling, but basically I'd probably buy one for a Steam machine if it came in at <=$350 for the barebones system (lacking SSD/HDD, RAM, and WiFi like the NUC and Brix systems do).
jasonelmore - Friday, January 17, 2014 - link
F that man, by the time you put a SSD RAM and wifi card, external drive, your in the $700-$900 range. just try building one of those Brix or NUC systems with reasonable components. You pay a premium for the low power consumption and small desktop footprint.smartypnt4 - Friday, January 17, 2014 - link
See, I'd be fine spending that kind of money on something that basically had a 7870 in a box the size of a Gigabyte Brix Pro. It's certainly not going to eb high-colume, but I can see a use case for it.Also, switching that to a HDD for $60 or so, using 8GB of RAM for $80, and forgoing the WiFi and external disc drives (neither are strictly necessary, each add ~$30) brings it to $490 for the whole system if they price it at $350. That seems reasonable to me given that current consoles aren't far off that, and you get better silicon than they have (Steamroller vs. Bobcat cores mainly).
Computer Bottleneck - Friday, January 17, 2014 - link
Yes, for a machine with these desktop APUs I would prefer a slightly larger form factor for the cost savings.Something the size of a Gateway SX, Dell Inspiron 660s, Lenovo H530s would work. These are systems can be found for as low as $350 on sale with a Haswell Core i3, 4GB RAM, 1TB HDD, Optical drive, Wifi, Windows 8.
Unfortunately for AMD I did not see them make any breakthroughs in value desktop for the Richland APUs. In almost every case an A8-6500 APU prebuilt was priced well above what the Core i3 systems were selling for. Hopefully this changes for the A8-7600 as I would like to see it priced more on par with the Haswell Core i3.
Alexvrb - Sunday, January 19, 2014 - link
Especially since the 7600 proved to be a good performer, whether at 65W or 45W. I think OEMs will like the flexibility this chip offers over its (distinctly 45W or 65W only) Richland counterparts. The higher TDP chips were actually a bit of a disappointment by comparison (considering shader count), at least with the memory configurations they were tested at. I'd really like to see the "K" models tested with faster memory. There's even an AMD branded set of 2400 DDR3 memory available now - that's like "wink wink hint hint it's an unlocked model".Mr Perfect - Friday, January 17, 2014 - link
That's the problem I have with this idea, though. It would be a fun toy, but I don't need one and I certainly wouldn't pay much for it. Even using it as a Steam box would be a stretch, the current offering of mITX-sized Steam boxes would be faster. Why would AMD want to spend a lot of R&D making a low-margin niche product?
If it was in a 35-45watt laptop it would be a different story of course.
Mr Perfect - Friday, January 17, 2014 - link
And in other news, using the italics tag forces a line return before and after the italicized word...dbwells - Friday, January 17, 2014 - link
I thought you were just being artistic.smartypnt4 - Friday, January 17, 2014 - link
I completely concur that the market for such a small desktop would be by definition a niche. However, if they're already designing such a thing for a laptop, why not allow the clocks to ramp a bit and throw it in a NUC or Brix sized system? I'd wager Intel put out the NUC as part a technology demonstration and part to force OEMs to start critically looking at what you can do with current processors. They certainly didn't put it out to be a high-volume product. They just had the work done and threw it in a case I'd bet. AMD could do something similar, but their pockets aren't quite as deep as Intel's, so they might not.yelped - Thursday, January 16, 2014 - link
It would be great for boutique builders and marketing."Design your own XBox One/PS4 PC"!