X570 Exposed: Up to Sixteen PCIe 4.0 Lanes, Flexible I/O

Updated: Sep 12, 2020

This is not the X470 replacement you were looking for, at least according to my conversations with AMD, at any rate.

The X570 is not a replacement for the X470, but instead slots in at a higher tier.

That means the firm’s X470 will soldier on as a value-oriented alternative to high-priced X570 models, and we may even see new X470 boards with updated layouts and features targeting people who can’t justify X570 premiums.

But this “model up” philosophy provides a reason for AMD to kill PCIe 4.0 graphics support on future X470 motherboards: Anyone who wants that pathway from the CPU to the GPU will likely be forced to buy an X570 board, unless they use hacked firmware.

It’s not in AMD's interest to produce a separate AGESA for the new X470 motherboards (though I guess that this could change...).

In the meantime, I spent some time to firm up the device connection limits for the X570 PCH, producing a block diagram from real-world application data.

The first thing most in-the-know geeks will notice is that the PCH supports eight USB 3.2 Gen1 (5Gb/s) pathways rather than four Gen2 (10Gb/s), and then they’ll notice that it also supports eight SATA 6Gb/s ports rather than two or even four.

That may seem odd since the X570 PCH is nothing more than a 14nm variant of the 12nm I/O die inside the Ryzen 3000-series processors, but it simply appears that the I/O die’s pathways are far more flexible than previously disclosed.

A little creative destruction rids the PCH version of the CPU’s memory controller and any unnecessary appendages, as each of those maximum connections must be selectively reduced by the motherboard manufacturer to fit everything into a combined 16 High-Speed Platform Lanes.

That may be just as well since device bandwidth is shared over a single PCIe 4.0 x4 connection to the CPU, though we have to at least give AMD credit for doubling that over its previous PCIe 3.0 version.

I'm fairly certain that the second CPU-based NVMe connection shown by AMD at its E3 Press Event should have been a breakout of the first, since motherboard manufacturers have only been able to get one PCIe 4.0 x4 NVMe interface directly from the CPU.

A total of 24 CPU lanes that include sixteen lanes for graphics, four for storage, and four for USB 3.x Gen2 conforms to AMD's statement that "High-Speed Platform Lanes defined as the sum of GPP PCI Express lanes, SATA ports, and USB ports from the chipset and processor that can be used concurrently."

Regarding the PCH, those same motherboard firms are extracting up to eight SATA ports from the PCH in addition to a second and third PCIe 4.0 x4 M.2 slots, with the only resource exclusion being that those board's third expansion card slot is disabled when the third M.2 slot is enabled.

None of those manufacturers have been able to tap the PCH for Gen2 (10Gb/s) USB 3.x thus far, but are instead relying upon the four ports provided by the CPU to feed three I/O panel and one front-panel connector.

These details may explain the absence of the above image in the official slide deck AMD later provided.

I'll inspect final products to be certain about USB 2.0 count, since motherboard manufacturers occasionally double-count USB 2.0 by adding the backwards compatibility of USB 3.x ports.

Hmm, PCH, HSIO, now where have we heard that before?, IT Tech-Talk Blog focusing on AMD and Nutanix with Cloudy things

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