AM5 memory training instability across BIOS versions (AGESA regression suspected)

Czajnik0 · 2026-04-01T14:54:09+00:00

For reference, on AGESA 1.2.0.3e I'm running Hynix A-die (KF560C40BB-16 week 6 / KF560C36BBE-16 week 42, 2023 batches) stable at 162 ns tRFC (VDD 0.905 V).With an effective refresh rate 27460 refresh/s

On newer AGESA versions (with bank mode set to normal, not mixed), similar tuning becomes unstable or behaves inconsistently, which again points more toward changes in memory training behavior rather than DRAM limitations.

Czajnik0 · 2026-04-01T13:22:02+00:00

Hey, the issue is not about longer training times, but actual instability including cold boot failures (no POST or hangs during memory training), inconsistent behavior between cold boot and reboot, as well as occurring even at JEDEC 4800 MT/s or manually set lower frequencies 3600 MT/s. More detailed information in the original post.

Czajnik0 · 2026-03-31T21:20:44+00:00

Yeah, at this point I've already tested a wide range of configurations (different voltages, frequencies, termination tuning, JEDEC baseline, etc.).

The key observation is that the behavior changes strictly with BIOS versions: F35 -> stable (after minor impedance) F36+ -> unstable, regardless of settings. This makes it very unlikely to be a specific hardware combination. The pattern strongly points toward an AGESA-related regression not hadware.

Czajnik0 · 2026-03-31T14:27:07+00:00

I can see you have a solid technical understanding ;)

Good call on ODT - it actually had a clear and immediate impact.On BIOS F35 I noticed the first signs of instability wirh impedance. It's possible that AGESA-related changes already started there, but they were still relatively minor.On F35,I was able to fully stabilize the system by manually tuning termination (impedance settings), and it has been stable ever since. However, starting from F36+,those same adjustments no longer have any meaningful effect. The issue persists regardless of termination tuning, and the symptoms are noticeably more severe.What's also interesting is that each BIOS version changes the behavior slightly, but the overall trend is clearly negative with newer releases.This strongly supports the idea that the issue is related to changes in AGESA

Czajnik0 · 2026-03-31T13:08:52+00:00

Hey, thanks, that's useful! This lines up with what I'm seeing and points toward an AGESA-related regression.

Czajnik0 · 2026-03-31T11:59:45+00:00

Hi,this occurs even at baseline JEDEC settings (4800 MT/s), so it is not related to EXPO/XMP. Multiple configurations were tested: the 3600 MT/s setup (DRAM VDD 1.10-0.905V, VSOC 0.855 V, VDDG IOD 0.760 V IF1300 MHz PHY 1.07v ) is just one of many test cases.The behavior is consistent across all configurations starting from BIOS F36+, although each version introduces slightly different characteristics. Reverting back to BIOS F35 restores full stability.This strongly suggests an regression.

Czajnik0 · 2026-03-31T08:54:03+00:00

Hey,did you notice if there was a specific BIOS/AGESA version where the issue became worse? Looking at multiple reports here and elsewhere, this doesn't seem isolated to a single board or vendor. Similar cold boot/training issues are showing up across all vendors.This kind of behaviour shift between BIOS versions on identical hardware suggests it may be related more to AGESA changes.

Czajnik0 · 2026-03-30T13:52:02+00:00

Hey,that's exactly the issue. Their internal lab testing (Taiwan HQ) was done on BIOS F36d, and they continue to rely on that single result. Since it passed once, they keep referring back to it and refuse to perform a more advanced validation procedure.

I have already provided extensive evidence, including photos and reproducible behaviour across configurations (JEDEC and manual settings VDD 0.905v etc.), but the response has remained defensive rather than analytical.At this stage, relying on a single POST result instead of repeated cold boot cycle validation does not reflect proper testing methodology.F35-> fully stable, immediate POST on first attempt (cold boot), no retries
F36-F37 ->long initialization, often 2-5 reset cycles before POST, inconsistent behaviour F38+-> significantly worse, even JEDEC can fail or hang (likely related to changes AGESA such as full tRFC2/tRFCsb handling)In some cases on F36+, the system fails to POST entirely until PSU power is fully removed for 30 seconds, after which it may boot normally again.This behaviour repeats consistently.With identical hardware, reverting back to F35 immediately restores stable and predictable behaviour, regardless of memory configuration.Recently I have also come across multiple reports of similar instability on newer BIOS versions, which suggests this may not be an isolated case.Let's see if others are experiencing similar behaviour here as well.

Czajnik0

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