Dell OptiPlex 9020 SFF · Libreboot native raminit

The receive timing margin sat right at the failure threshold

Width of the “high region” for channel 0, byte 5 (the RCVET step of memory training) — the minimum across ranks for each boot attempt, from the COM1, 115200 8N1 console log. Failure threshold: ≤32. At 800 MHz it is exactly 32 in every layout. At 666 MHz the first boot still failed, then the margin grew to 40 and training passed even with 32 GB. Passing training is not the same as booting: 32 GB still hung later.

Memory training passed (width >32), which does not mean the system booted

RCVET failure (width =32)

Failure threshold

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Source: coreboot romstage serial logs collected September 21–23, 2026. Each point is a separate cold boot; between attempts the DRAM frequency (the DRAM_TCK_FLOOR patch) and the physical module layout were changed.