PSA: AMD is locking ECC UDIMM frequency on consumer AM5

Posted by ParanoidZoid@reddit | hardware | View on Reddit | 93 comments

TL;DR: If you are lucky enough to have ECC UDIMMs on AM5 and they're manufacturer rated above 5200 MT/s, AGESA ComboAM5 PI version Pre1.3.0.0 and later caps ECC UDIMM down to 5200 MT/s on Ryzen 9000 series consumer CPUs. It's an AMD-side change, and the cap seems to live in the signed PSP firmware, so board vendors can't override it. To keep running ECC above 5200, stay on AGESA 1.2.7.0 or earlier.

Confirmation from Asus

This warning now appears on every recent Asus AM5 BIOS download page (B650, B650E, X670, X670E, X870, X870E across PRIME, TUF, ROG Strix, etc.):

"Starting from AGESA ComboAM5 PI version Pre1.3.0.0*, ECC-UDIMM memory speed will be limited to 5200 MT/s when paired with 9000 series CPUs."*

And on the ROG forum X670/X870 resource thread, one of the Asus bios engineers said this directly:

"AMD limited the speed of ECC UDIMM dual rank to 5200 start with AGESA 1300 BIOS (It means Granite Ridge). This is not an ASUS issue. If you want a high clock speed can use the AGESA 1270 BIOS or need ecc disabled with new bios."

This problem is not limited to Asus by the way, other motherboard vendors (e.g. Asrock) are also experiencing the same issue.

BIOS inspection

Before Asus confirmed it was AMD side, I was inspired by someone else modding a BIOS using Claude. So I had Claude look into the BIOS files. The below is a summary from it, I had it run APCB parser and PSPTool.

The APCB Memory groups for the PSP IDs the 9800X3D actually reads (0xbc0d0300 and 0xbc0d0b00) are byte-identical between 3112 and 3603. Same DIMM tables, same platform tuning data. The UEFI CBS options are also unchanged: same speed selectors, same ECC submenu, same defaults.

The only meaningful change between the two firmwares is the ABL, which is AMD's signed PSP binary that drives memory training. Same APCB input, different speed output for ECC DR specifically. Non-ECC at 6000 still trains fine on 3603, which means there's ECC-specific logic in the training path that changed between AGESA versions, and it's in code nobody outside AMD can read or patch.

Notes from L1Techs Users

One open question: nobody has posted a clean test on Ryzen Pro 9000 yet. Would be interesting to see if these SKUs that officially advertise ECC support. If anyone here has access to that, it would be interesting to know if you're experiencing this limitation.

So what?

It's a niche within a niche, and at current RAM prices we should at least be thankful AMD still supports ECC on consumer CPUs at all as Intel doesn't even pretend to on theirs. What's puzzling is that this is only on Zen 5 but not Zen 4. Ideally AMD would just say something officially instead of leaving motherboard vendors like Asus to publish it as a footnote.

Links

https://forum.level1techs.com/t/asus-proart-x870-e-creator-wifi-and-ecc-memory-issue-on-newer-bioss/248534

https://rog-forum.asus.com/t5/amd-600-series/x670-x870-resource-thread/m-p/1145818/highlight/true#M11818

https://rog.asus.com/motherboards/rog-crosshair/rog-crosshair-x670e-hero-model/helpdesk_bios/

https://rog.asus.com/motherboards/rog-crosshair/rog-crosshair-x870e-apex/helpdesk_bios/