Wednesday, May 20th 2020
AMD "Renoir" Desktop APU Could Lack PCIe gen 4.0, Hints BIOSTAR B550 Motherboard Product Page
AMD's 4th generation Ryzen "Renoir" desktop APUs, based on the "Zen 2" microarchitecture, could lack PCI-Express gen 4.0, hints the product page of an upcoming AMD B550 chipset motherboard by BIOSTAR. AMD already declared that the B550 lacks support for "Picasso," which means the "Ryzen with Radeon Vega Graphics" processors referenced in the BIOSTAR product page have to be "Renoir." On the mobile platform, Ryzen 4000H and 4000U series processors do lack PCIe gen 4.0, but it was expected that AMD will enable gen 4.0 for the desktop socket AM4 platform.
The lack of gen 4.0 support has implications for "Renoir." For starters, the APU, like its predecessors, spares only 8 PCIe lanes toward PEG (PCI-Express discrete graphics, or the main x16 slot you typically use for graphics cards). If these lanes are gen 3.0, then even the newer graphics cards, such as AMD's "Navi" RX 5700 XT, or next-gen GeForce "Ampere," would have to make do with a PCI-Express 3.0 x8 interface, despite being gen 4.0 x16-capable. We will test just how much of a bottleneck this poses, when the next-gen graphics cards come out.The second implication specifically affects the platform. On some upcoming motherboards, such as the B550 AORUS Master by GIGABYTE, PCIe gen 4.0 lanes from the PEG slot are shared with a couple of additional M.2 slots. So, you'd be left with only one of the three M.2 slots functional, the topmost one that's directly wired to the AM4 socket, and at gen 3.0 speeds. Lastly, the lack of gen 4.0 means that the chipset-bus between "Renoir" and both the B550 and X570 will be PCI-Express 3.0 x4. With "Matisse" or "Vermeer," the bus runs at PCI-Express 4.0 x4 speeds.
Sources:
momomo_us (Twitter), BIOSTAR Product Page
The lack of gen 4.0 support has implications for "Renoir." For starters, the APU, like its predecessors, spares only 8 PCIe lanes toward PEG (PCI-Express discrete graphics, or the main x16 slot you typically use for graphics cards). If these lanes are gen 3.0, then even the newer graphics cards, such as AMD's "Navi" RX 5700 XT, or next-gen GeForce "Ampere," would have to make do with a PCI-Express 3.0 x8 interface, despite being gen 4.0 x16-capable. We will test just how much of a bottleneck this poses, when the next-gen graphics cards come out.The second implication specifically affects the platform. On some upcoming motherboards, such as the B550 AORUS Master by GIGABYTE, PCIe gen 4.0 lanes from the PEG slot are shared with a couple of additional M.2 slots. So, you'd be left with only one of the three M.2 slots functional, the topmost one that's directly wired to the AM4 socket, and at gen 3.0 speeds. Lastly, the lack of gen 4.0 means that the chipset-bus between "Renoir" and both the B550 and X570 will be PCI-Express 3.0 x4. With "Matisse" or "Vermeer," the bus runs at PCI-Express 4.0 x4 speeds.
27 Comments on AMD "Renoir" Desktop APU Could Lack PCIe gen 4.0, Hints BIOSTAR B550 Motherboard Product Page
pitchforkstorches :shadedshu:Since, different to Intel, AMD does not produce more differing wafer masks than absolutely necessary it is very probable that desktop Renoir is completely the same silicon as the notebook one, resulting in PCIe 3.0 just being all there is inside the chip.
B550 description is copypasted from X570 board. X570 supports Picasso and Raven ridge.
Also, I'm not sure the underlying assumption (B550 doesn't support Picasso) applies. The blogosphere seemed to ignore that despite AMD not supporting 3rd gen Ryzen on 1st gen AM4 chipsets like x370/b350 boards, most of those boards received and supported 3rd gen Ryzen bios updates no problem. It is therefore quite likely motherboard manufacturers will provide unofficial support to older processors and therefore that guidance may be directed at Picasso, and will be updated when Renoir on desktop is actually released.
btarunr > AMD already declared that the B550 lacks support for "Picasso," which means the "Ryzen with Radeon Vega Graphics" processors referenced in the BIOSTAR product page have to be "Renoir." On the mobile platform, Ryzen 4000H and 4000U series processors do lack PCIe gen 4.0, but it was expected that AMD will enable gen 4.0 for the desktop socket AM4 platform.
Renoir is a mobile part, first and foremost, and the X570 with PCIe 4.0 demands active cooling for its 15-20W power draw. That kind of power consumption has no part being within a mile of any parts aimed at the 15W laptop market.
I don't know how much power CPU PCIe 4.0 on the existing Picasso dies uses, but based on the chipset draw, I'm going to take a guess that it's not trivial.
It's almost as if all these people somehow expect AMD to compete against Intel and Nvidia while somehow not doing any of the competitive actions Intel and Nvidia does... You can't have it both ways..... Either AMD competes at the highest level with cutthroat tactics, or (as a lot of people have acted lately) they're a non-profit charity solely created to fulfill the every whim of whatever "enthusiast" whines the loudest and as a ridiculous sense of entitlement.
Here's my first point: why would an APU, designed to NOT BE USED WITH A DGPU, need x16 lanes? You want x16 lanes and 8 cores? AMD ALREADY HAS A PRODUCT FOR THAT, the 3600,3700x, etc.... The only people I can see complaining about an APU not having x16 lanes are a scumbags who thought they'd get one over on AMD by picking up one of these APUs for cheaper than a 3700x and pairing it with a dGPU... And I'm sure it'll be the scumbags crying the loudest. What's next? Complaining about a mITX board only having one PCIe slot? "I'm entitled to AMD fulfilling my every desire no matter how unrealistic"
Jeez, whomever wrote this article is doing nothing but being sensational and trying to stoke the fires because other than demonstrating a ridiculous sense of entitlement (the article basically implies that AMD should do everything we want, no matter how ridiculous, or suffer our scorn) I don't understand the goal of this article.
I can't help but think, that if some of these crybabies had put some of this pressure on Intel of Nvidia at least once in the past decade, maybe things would be generally better for the community, but instead when when Intel and Nvidia pull shady stuff, everyone just bends over and asks for seconds.
I'm not trying to defend AMD as much as I'm trying to defend competition... This is a critical time for AMD, they need to capitalize as much as they can and as fast as they can in order to build up a war chest so that thry have the financial power necessary to come back at Intel when Intel INEVITABLY answers back. If AMD is hamstrung now, then the past few years of glorious and beneficial competition could come to an end and we'll find ourselves back in the dystopia before Ryzen launched and if I'm ever forced to buy a stagnated CPU with incremental gains every year for $500, I'll swear off PC altogether.
We get this pciex dramma.
So apparently pciex does matter but only when AMD'S is questionable.
I bet every intel review on here says you don't need pciex4.
PCIe 4.0 is about storage, and honestly there's not yet enough on the market to make consumers buying a budget B-series motherboard worry about it. It matters to X570, Z490, and it matters to X399 - and even then, only if the machine in question is going to need multiple PCIe 4.0 SSDs which is extremely unlikely whilst still qualifying as "consumer" workloads.
I could make some dramma for myself by buying a 5600Xt then trying to game on max settings at 4k like I would if I was a click bait generator.
It will nonetheless be interesting to see how Renoir's PCIe lanes are routed for desktop chips given that they in one way have more PCIe than the CPUs. Zen 2 CPUs have one x16 "PCIe graphics" block + one x4 block for storage (of course these designations are rather meaningless; a GPU can run just fine off an m.2 adapter should you want to, and the x16 can be bifurcated and used for storage). Renoir has an x8 PEG block, but two x4 storage blocks (that can either act as 4x SATA or PCIe 3.0 x4). Will it even be possible to utilize all of this on a desktop platform designed around a two-block PCIe lane setup (which AM4 has always had)? Where will the last x4 block be routed to? Are there free pins on the AM4 socket that could be routed to an APU-only m.2 slot on new boards, or some setup where those lanes are otherwise utilized? Or will this x4 block take on the role of the chipset uplink, which seems to be absent from AMD's own Renoir block diagrams?
This compatibility issue could be also a cause for AMD to not use Navi but Vega.
This decision could indeed hinder the use of PCIe4 for Renoir completely, but thats speculative also.
AMD has PCIe4 controllers on 12nm (io chiplet) and 7nm (navi), so there is no any reasons to limit Renoir with PCIe3 except TDP.
I wouldn't argue it couldn't be the case any I tried worked ok but I haven't bothered in a while.
But that's a niche not many will have troubles with.
AMD Ryzen series CPUs (Matisse)
- 2 x PCI Express x16 Slots (PCIE1: Gen4x16 mode; PCIE3: Gen3 x4 mode)*
AMD Ryzen series APUs (Renoir)
- 2 x PCI Express x16 Slots (PCIE1: Gen3x16 mode; PCIE3: Gen3 x4 mode)*