nixos-servers/docs/plans/pn51-stability.md

ASUS PN51 Stability Testing

Overview

Two ASUS PN51-E1 mini PCs (Ryzen 7 5700U) purchased years ago but shelved due to stability issues. Revisiting them to potentially add to the homelab.

Hardware

	pn01 (10.69.12.60)	pn02 (10.69.12.61)
CPU	AMD Ryzen 7 5700U (8C/16T)	AMD Ryzen 7 5700U (8C/16T)
RAM	2x 32GB DDR4 SO-DIMM (64GB)	1x 32GB DDR4 SO-DIMM (32GB)
Storage	1TB NVMe	1TB Samsung 870 EVO (SATA SSD)
BIOS	0508 (2023-11-08)	Updated 2026-02-21 (latest from ASUS)

Original Issues

• pn01: Would boot but freeze randomly after some time. No console errors, completely unresponsive. memtest86 passed.
• pn02: Had trouble booting — would start loading kernel from installer USB then instantly reboot. When it did boot, would also freeze randomly.

Debugging Steps

2026-02-21: Initial Setup

1. Disabled fTPM (labeled "Security Device" in ASUS BIOS) on both units
   • AMD Ryzen 5000 series had a known fTPM bug causing random hard freezes with no console output
   • Both units booted the NixOS installer successfully after this change
2. Installed NixOS on both, added to repo as pn01 and pn02 on VLAN 12
3. Configured monitoring (node-exporter, promtail, nixos-exporter)

2026-02-21: pn02 First Freeze

• pn02 froze approximately 1 hour after boot
• All three Prometheus targets went down simultaneously — hard freeze, not graceful shutdown
• Journal on next boot: system.journal corrupted or uncleanly shut down
• Kernel warnings from boot log before freeze:
  • TSC clocksource unstable: Marking clocksource 'tsc' as unstable because the skew is too large — TSC skewing ~3.8ms over 500ms relative to HPET watchdog
  • AMD PSP error: psp gfx command LOAD_TA(0x1) failed and response status is (0x7) — Platform Security Processor failing to load trusted application
• pn01 did not show these warnings on this particular boot, but has shown them historically (see below)

2026-02-21: pn02 BIOS Update

• Updated pn02 BIOS to latest version from ASUS website
• TSC still unstable after BIOS update — same ~3.8ms skew
• PSP LOAD_TA still failing after BIOS update
• Monitoring back up, letting it run to see if freeze recurs

2026-02-22: TSC/PSP Confirmed on Both Units

• Checked kernel logs after ~9 hours uptime — both units still running
• pn01 now shows TSC unstable and PSP LOAD_TA failure on this boot (same ~3.8ms TSC skew, same PSP error)
• pn01 had these same issues historically when tested years ago — the earlier clean boot was just lucky TSC calibration timing
• Conclusion: TSC instability and PSP LOAD_TA are platform-level quirks of the PN51-E1 / Ryzen 5700U, present on both units
• The kernel handles TSC instability gracefully (falls back to HPET), and PSP LOAD_TA is non-fatal
• Neither issue is likely the cause of the hard freezes — the fTPM bug remains the primary suspect

Benign Kernel Errors (Both Units)

These appear on both units and can be ignored:

• clocksource: Marking clocksource 'tsc' as unstable — TSC skew vs HPET, kernel falls back gracefully. Platform-level quirk on PN51-E1, not always reproducible on every boot.
• psp gfx command LOAD_TA(0x1) failed — AMD PSP firmware error, non-fatal. Present on both units across all BIOS versions.
• pcie_mp2_amd: amd_sfh_hid_client_init failed err -95 — AMD Sensor Fusion Hub, no sensors connected
• Bluetooth: hci0: Reading supported features failed — Bluetooth init quirk
• Serial bus multi instantiate pseudo device driver INT3515:00: error -ENXIO — unused serial bus device
• ata2.00: supports DRM functions and may not be fully accessible — Samsung SSD DRM quirk (pn02 only)

Next Steps

• Monitor both units for stability (fTPM disabled on both, BIOS updated on pn02)
• If either freezes again, try adding tsc=unstable kernel parameter (unlikely to help but easy to rule out)
• If freezes continue, try disabling unused hardware in BIOS (GPU, WiFi, Bluetooth, audio)
• If still freezing, may be a hardware defect
• Once stable: add second RAM stick back to pn02, reinstall with NVMe