AMD 7th Gen Bristol Ridge and AM4 Analysis: Up to A12-9800, B350/A320 Chipset, OEMs first, PIBs Later
by Ian Cutress on September 23, 2016 9:00 AM ESTUnderstanding Connectivity: Some on the APU, External Chipset Optional
Users keeping tabs on the developments of CPUs will have seen the shift over the last ten years to moving the traditional ‘northbridge’ onto the main CPU die. The northbridge was typically the connectivity hub, allowing the CPU to communicate to the PCIe, DRAM and the Chipset (or Southbridge), and moving this onto the CPU silicon gave better latency, better power characteristics, and reduced the complexity of the motherboard, all for a little extra die area. Typically when we say ‘CPU’ in the context of a modern PC build, this is the image we have, with the CPU containing cores and possibly graphics (which AMD calls an APU).
Typically the CPU/APU has limited connectivity: video outputs (if an integrated GPU is present), a PCIe root complex for the main PCIe lanes, and an additional connectivity pathway to the chipset to enable additional input/output functionality. The chipset uses a one-to-many philosophy, whereby the total bandwidth between the CPU and Chipset may be lower than the total bandwidth of all the functionality coming out of the chipset. Using FIFO buffers, this is typically managed as required. The best analogy for this is that a motorway is not 50 million lanes wide, because not all cars use it at the same time. You only need a few lanes to cater for all but the busiest circumstances.
If the CPU also has the chipset/southbridge built in, either in the silicon or as a multi-chip package, we typically call this an ‘SoC’, or system on chip, as the one unit has all the connectivity needed to fully enable its use. Add on some slots, some power delivery and firmware, then away you go.
Bristol Ridge’s ‘SoC’ Configuration
What AMD is doing with Bristol Ridge is a half-way house between a SoC and having a fully external chipset. Some of the connectivity, such as SATA ports, PCIe storage, or PCIe lanes beyond the standard GPU lanes, is built into the processor. These fall under the features of the processor, and for the current launch is a fixed set of features. The CPU also has additional connectivity to an optional chipset which can provide more features, however the use of the chipset is optional.
Here’s a block diagram to help explain:
On the APU we have two channels of DDR4, supporting two DIMMs per channel. For the major PCIe devices, we have a PCIe 3.0 x8 port, and this does not support bifurcation (or splitting) to any x4, x2 or x1 combination. It’s a solitary x8 lane suitable for a PCIe x8 port (we’ll discuss what else can be done with this later). The APU communicates with the optional chipset with a PCIe 3.0 x4 link, and we’ve confirmed with AMD that this is a simple PCIe interface. The other parts of the APU give four USB 3.0 ports, two SATA 6 Gbps ports, and two PCIe 3.0 x1 ports. These ports also support NVMe, and can provide two PCIe 3.0 x1 storage ports or can be combined for a single PCIe 3.0 x2.
It Looks Like an x16
Now, if you look at the layout, try counting up how many PCIe lanes are split across all the features. We’ve seen a USB 3.0 hub support four ports of USB 3.0 from a single lane of PCIe 3.0 before, and there are plenty of controllers out there that split a PCIe 3.0 x1 into two SATA ports. So play the adding game: x8 + x4 + x1 + x1 + x1 + x1 = x16. The Bristol Ridge APU seems to suggest it actually has sixteen PCIe 3.0 lanes, but AMD has decided to forcibly split some of them using internal hubs and controllers.
It’s an interesting tactic because it means that systems can be built without a discrete chipset, or the four chipset lanes can be used for other features. However it negates a full PCIe 3.0 x16 link for a full-bandwidth PCIe co-processor. Bearing in mind that if there was a PCIe 3.0 x16 link, there are no additional lanes for a chipset, so there would not be any IO such as SATA ports anyway, such that there would be no physical storage.
The x16 total theory is also somewhat backed up by the lack of bifurcation on the x8 link. Historically a PCIe root complex in a consumer platform that supports x16 can be bifurcated down to x8/x4/x4, and anything else requires additional PCIe switches to support more than three devices. It would seem that AMD has taken the final x4 link and added an on-die PCIe switch to provide those ports, for standard PCIe to USB/SATA controllers. I would hazard a guess and say that what AMD has done is more integrated and complicated than this, in order to keep die area low.
PCIe is Fun with Switches: PLX, Thunderbolt, 10GigE, the Kitchen Sink
Another thing about the x8 link is that it can be combined with an external PCIe switch. In my discussions with AMD, they suggested a switch that bifurcates the x8 to dual x4 interfaces, which could leverage fast PCIe storage while maintaining the onboard graphics for any GPU duties. There’s the other side, in using an x8 to x32 PCIe switch and affording two large x16 links. However, large GPU CrossFire is not one of the main aims for the platform.
Here’s a crazy mockup I thought of, using a $100 PCIe switch. I doubt this would come to market.
Ian plays a crazy game of PCIe Lego
The joy of PCIe and switches is that it becomes a mix and match game - there’s also the PCIe 3.0 x4 to the chipset. This can be used for non-chipset duties, such as anything that takes PCIe 3.0 x4 like a fast SSD, or potentially Thunderbolt 3. We discussed TB3 support, via Intel’s Alpine Ridge controller, and we were told that the AM4 platform is currently being validated for systems supporting AMD XConnect, which will require Thunderbolt support. AMD did state that they are not willing to speculate on TB3 use, and from my perspective this is because the external GPU feature is what AMD is counting on as being the primary draw for TB3 enabled systems (particularly for OEMs). I suspect the traditional motherboard manufacturers will offer wilder designs, and ASRock likes to throw some spaghetti at the wall, to see what sticks.
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ddriver - Saturday, September 24, 2016 - link
So you are a fascist who thinks some people are not entitled to opinions? I am not projecting anything, I am expressing my opinion. If you have a problem about it, that's your problem entirely. If my opinions threaten to shatter someone's fragile artificial worldview, that's their their problem entirely. Or maybe you are implying that people should only be allowed to express opinions that are coherent with the herd's baaing? Did you see me denying the right of opinions to dummies or anyone? Nah, because it is their right, even if it is mind-numbingly stupid and even if I don't like it.goatfajitas - Friday, September 23, 2016 - link
Different ballparks entirely dood. One runs alot of fun mobile toys, the other runs the entire business world including every computer and every system in every factory that makes all of those toys.ddriver - Friday, September 23, 2016 - link
That's not the problem, most people can't and quite frankly don't need to be powerusers - engineers, designers and such are a very small fraction of the population. The problem is the lack of choice - you don't even have the option to use an android or apple tablet for professional work. And the even bigger problem - that this becomes a trend.Year after year the entire industry is moving towards the "walled garden spyware milking station" model, I wouldn't be surprised if in the near future owning an open general purpose computer becomes criminalized - because you know... only pirates, hackers, terrorists and pedophiles need it.
And last but not least, what is perhaps most worrying is people are getting increasingly dumb as technology gets more and more affordable. One would say "big whoop, I don't care about the dummies", however in the long run that's a huge problem, it affects the entire species, and thus every individual member of it. Call me old fashioned, but I think people should, if not get smarter, then at least not get dumber as technology becomes more available and widespread. Today software helps you finish your sentences, before you know it, software will be dictating your sentences. It is ok for machines to do the "legwork" for you - numerous small and repetitive tasks, but it is a very dangerous thing when machines begin doing the thinking for you and you forget how to do it... if you ever knew to begin with...
goatfajitas - Friday, September 23, 2016 - link
I don't disagree with most that... but I don't know if people are getting increasingly dumb... It used to be the dumber people didn't use computers much, and now everyone does. As computer/tablet/mobile usage went up the average computer user's IQ went down, but those dumbies always existed, its just that now they are online and have a voice.... Yadda yadda yadda, now we have Trump. LOLddriver - Friday, September 23, 2016 - link
They are being made dumber and it makes perfect sense. Longterm economic strategy 101 - with ample resources you breed a lot of workers to produce wealth, as resources begin to run out you automate menial labor and focus on services to take that wealth from the workers, and finally, using the wealth you produce a military complex to protect you from the workers as they become obsolete and infeasible both as workers and consumers. Being dumb will make it easy to march the general population straight into the void, unable to resist or survive without the system which no longer has need of them. Dumb is convenient - easy to exploit, easy to dispose of. More technology has allowed for more ways to dummify - more knowledge of the dummies, more control over the dummies, more distraction for the dummies from the issues at hand. Everything people do online passes through data mining algorithms, gets profiled, analyzed, and combed for anything anyone might find useful in any way. Including this very comment space.goatfajitas - Friday, September 23, 2016 - link
I agree, there are a heck of alot of dumb people out there... Just not sure they are getting even dumber. Lazier maybe, but the average person has always been mindbogglingly stupid.Just picture in your mind how stupid the average person is... Now think, half of everyone is stupider than that guy! - George Carlin (said long before the vast majority of people had any PC at all)
msroadkill612 - Wednesday, April 26, 2017 - link
Its sad to think almost 50% of people are below average.msroadkill612 - Wednesday, April 26, 2017 - link
Sadly, i concur. Its depressing.A way of looking at it via the "property is theft" philosophy is why, w/ all these new marvels, are even the fortunate employed (those serfs useful to the regime), feeling more on a treadmill over a shark tank than ever?
Our alleged protective regimes have focused more on how to meter mankinds recent gifts (and infrastructure, long paid for by our compatriot forbears), than disperse them free or at cost.
Most of the great "inventions" and their resultant fortunes were assigned to the best schemer in the group, not the true inventors. Some were unrelated predatory lawyers, & often they were major hinderances to wider adoption.
The last thing capitalism wants is to remove the necessity of serving the regime.
To all intents, it is illegal to live simply. You may not build your own shelter e.g. You must take a mortgage for a sale price bureaucrats very actively inflate.
Free wi-fi to the poor in some areas would cost a pittance to our allegedly caring commonwealths. Instead they hand out monopolistic licences at dodgy auctions, if that.
Michael Bay - Saturday, September 24, 2016 - link
You really have to be braindead or commited ethnic masochist to support anyone but Trump in this cycle.Valantar - Saturday, September 24, 2016 - link
"Commited ethnic masochist". Did you mean to say "not astoundingly racist"? Because those words you just strung together mean nothing at all.Also, braindead? Really? So anyone with a functioning brain would be unable to see the lying, gross inconsistency, thin-skinnedness and general stupidity that spews from the Trump campaign (and his own mouth)? Not to mention the racism, sexism, homophobia, transphobia, elitism, disdain for poor/middle class people, blatant disregard for the rule of law, due process and the courts, promotion of violence, and willingness to lie about anything and everything to win?