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What a HyperTransport sync flood means
HyperTransport is a high-speed link used to connect components in some platforms. A sync flood is a fault-containment response: on documented Sun Fire systems, the machine resets and retains error information so it can be reported at the next boot. Oracle describes the behavior this way: “Sync floods on HyperTransport links, the machine resets itself, and error information gets retained through reset.” Oracle Sun Fire diagnostics documentation Red Hat also documents the message after unexpected reboots on Sun Fire X4200 systems. Red Hat documentation
The exact POST message documented by Oracle is: “A Hyper Transport sync flood error occurred on last boot, press F1 to continue.” Seeing it means the system recorded an event on the previous boot; pressing F1 continues startup but does not identify or repair the cause.
What can trigger the error
The message can be associated with several fault classes, so it does not by itself prove that the motherboard, RAM, or CPU must be replaced.
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- HyperTransport link faults: a link or CRC error may trigger the reset response.
- PCI bus errors: a PCI SERR (system error) or PERR (parity error) can be involved.
- Uncorrectable DRAM ECC errors: Oracle notes that the sync-flood mechanism prevents erroneous data from propagating over HyperTransport links.
- Unsupported or incorrectly installed DIMMs: memory type or population can be incompatible with the platform.
- CPU microcode loading during POST: after a CPU change, a separate BIOS POST microcode error may occur if the BIOS cannot load microcode for that CPU. Oracle says the BIOS must be updated in this case.
- A platform-specific PCI/MMIO mapping issue: Oracle documents an X4240/X4440 fault in which a HyperTransport link protocol error can indicate a low-4-GB PCI/MMIO mapping overlap or discrepancy.
Check the event records before changing hardware
On the relevant Sun Fire platforms, the event may appear in DMI and the service processor’s system event log (SEL). Export or record those entries before clearing logs: the timestamps and accompanying ECC, PCI, thermal, or link events can help distinguish a memory fault from a bus or firmware problem.
- Write down the exact system model, installed CPU, BIOS revision, DIMM part numbers and layout, and any recent hardware or firmware changes.
- Record whether the error followed a cold boot, a reboot, or a high-I/O workload.
- Export the DMI and service-processor SEL entries, then correlate their timestamps with other recorded errors.
- Only after preserving the records, proceed with controlled troubleshooting.
Troubleshoot from reversible checks to part replacement
- Restore supported stock settings. Remove overclocking and undervolting while diagnosing; return CPU, memory, and HyperTransport settings to values supported by the platform.
- Check compatibility. Verify that the CPU and DIMM type and population are supported by the system and its installed BIOS. If a CPU was recently changed and the logs identify a microcode POST problem, install the correct BIOS update for that platform.
- Inspect or isolate hardware carefully. Reseat or test memory and expansion hardware only as directed by the platform’s service manual. Change one component at a time where the manual permits, and note whether the event follows the component or configuration.
- Replace only an identified part. Use the event records and an isolation test to identify the failing field-replaceable unit (FRU) before buying a DIMM, CPU, or motherboard.
For the specific X4240/X4440 mapping fault documented by Oracle, briefly removing all AC cords is described as a way to reset the service processor and motherboard. This is model- and fault-specific; it is not a general fix for sync-flood errors. Follow the applicable service documentation and power-safety procedures.
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Does the error mean you need a BIOS update or new RAM?
Not necessarily. A BIOS update is indicated when the evidence points to the documented CPU microcode POST issue or when the platform’s compatibility guidance requires a newer BIOS for the installed CPU or memory. RAM replacement is justified when ECC records or a supported memory test identifies a DIMM or memory fault. A motherboard or CPU replacement should likewise follow evidence that isolates that FRU, rather than the sync-flood text alone.
There is no general failure-rate statistic or cost figure established for this error. Because the same message spans multiple fault classes and hardware compatibility is model-specific, use the system’s service manual and verified FRU information rather than choosing a generic replacement part.
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