### Human: Can you tell about Debugging ESX Machine Check Exception (MCE) PSOD. ### Assistant: This article describes how to debug ESX Machine Check Exception (MCE) purple diagnostic screen (PSOD) with an example.. ESXi servers may halt with a purple diagnostic screen (PSOD) due to MCE (machine check exception) errors. MCE errors are due to hardware issues.

The MCE purple diagnostic screen displays multiple things. Out of these, the MCi_STATUS register is useful in debugging the problem.

Register Details:

The MCi_STATUS register consists of information about the machine check error.The register is displayed next to the “S:” as shown in the example below:
	MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
	
	Bits and their significance:

	6362616059585753-5638-5232-3716-310-15VALID flag – If set, then information is validOVERFLOW flag – If set, then may indicate multiple MCEs occurred close to each otherUNC flag- If set, then CPU could not correct the errorEN flagMISCV flag – If set, then MISC register contains more informationADDRV – If set, then the ADDR register contains where the error occurredPCC flag- If set, then it means processor may have been corrupted.Architectural if bit 11 is set, else “other information”Architectural if bit 10 is set, else “other information”Other informationModel specific error code for CPUMachine check error code
	

To debug the error, the low 16 bits of the MCi_STATUS register are important. These bits indicate a simple or compound error.

Option 1: Using Automatic Tool

NOTE: You can now debug the error with the following tool that automates the steps below:
	https://vmware-psod-reader.github.io/vmware-psod-reader/
	

Option 2: Using Manual Steps

Simple errors are easy to debug
	MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
	Compound errors
	MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5

	F – Form flag
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5

		Filtering means that some or all of the subsequent corrections to this entry in this structure are not posted.
		TT - Applies to 2 and 4 above.
		Indicates type of transaction:

		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		LL - Applies to 1, 2, 4 and 5 above.
		Indicates the level in the memory hierarchy where the error occurred.

		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		RRRR - Indicates type of action associated with the error. Actions are:
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		PP (Participation) - Describes the role of the local processor in the error.
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		T (Time-out) - 1 = Request timed out.II (Memory or I/O)
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		Memory Controller errors - Defined by MMM and CCCC subfields above.MMM – Memory error
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		CCCC – Channel with the error
		MC: PCPU18 B:13 S:0xfe20004000011166 M:0x7246040086 A:0x38c989b100 5
		
	. Here is an example of how to analyse an MCE purple diagnostic screenshot:



Note down the MCi_STATUS register value is 0xfe20004000011166.Convert it to binary:
	1111 1110 0010 0000 0000 0000 0100 0000 0000 0000 0000 0001 0001 0001 0110 0110
	Take the lower 16 bits of the MCi_STATUS register:
	1111 1110 0010 0000 0000 0000 0100 0000 0000 0000 0000 0001 0001 0001 0110 0110

	Compare it with the compound errors. In this case, this appears to be a cache hierarchy error (type 4).
	Apply the values:
	1111 1110 0010 0000 0000 0000 0100 0000 0000 0000 0000 0001 0001 0001 0110 0110
	

Conclusion:

It looks like the purple diagnostic screen occurred while there was a prefetch operation on some data in the L2 cache of the processor.Thus, this could be a problem with the L2 cache on the processor.Therefore, we should replace the CPU first and check if the issue is resolved. In case the issue comes up again, we could replace the motherboard.. ### Human: Now explain this as a Nutanix support agent summarizing the answer step by step. In case, you don't know the answer say - I don't know.