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You are here: MacNN Forums > Hardware - Troubleshooting and Discussion > Mac Desktops > Memory Parity Errors

Memory Parity Errors
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bobpalmer
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Dec 5, 2009, 05:56 AM
 
Does anyone know how to decipher the panic log to determine which memory DIMM is having a parity error? My system was crashing several times a week with parity errors. TechTool reported no problems with memory. After the last failure, one of the DIMM's became invisible to the system. System Profiler reported Slot 5 as empty, and my 8GB machine now said it only had 6GB of RAM. This is a new Mac Pro system, so once I had a hard failure I took the machine back to Apple for repair.

The panic log has a DIMM field, but it is always 0. I'm assuming it is not real data. The bad DIMM was in slot 5.
Here is the memory section from the log:
Package 1 logged:
IA32_MC8_STATUS(0x421): 0xbe0000000001009f valid
Channel number: 15 (unknown)
Memory Operation: read
Machine-specific error: Read ECC
COR_ERR_CNT: 0
Status bits:
Processor context corrupt
ADDR register valid
MISC register valid
Error enabled
Uncorrected error
IA32_MC8_ADDR(0x422): 0x0000000143dec640
IA32_MC8_MISC(0x423): 0xfa5dd76400005840
DIMM: 0
Channel: 0
Syndrome: 0xfa5dd764
MacPro 2x 2.93GHz Quad-Core Intel Xeon
Power Mac 4x 2.5GHz G5 (SETI #1 RAC May 4, 2006)
Power Mac 2x 1GHz G4
     
ghporter
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Dec 5, 2009, 10:42 AM
 
The log says "DIMM: 0," which indicates exactly which DIMM is giving you problems.

Glenn -----OTR/L, MOT, Tx
     
bobpalmer  (op)
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Dec 6, 2009, 12:14 AM
 
System Profiler reports Memory Slots DIMM 1 through DIMM 8. The failing memory was in slot DIMM 5. How does DIMM 0 map into DIMM 5? Do you have a mapping list between DIMM slots that would appear in the panic log to DIMM slots as shown by System Profiler and the CoreServices/Memory Slot Utility.app?
MacPro 2x 2.93GHz Quad-Core Intel Xeon
Power Mac 4x 2.5GHz G5 (SETI #1 RAC May 4, 2006)
Power Mac 2x 1GHz G4
     
ghporter
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Dec 6, 2009, 10:40 AM
 
That's quite odd. If the error message said "DIMM 0," then it should have referred to the first slot. Unless it was "DIMM 0, Bank 2," which would be the 5th slot, I don't know why it was actually slot 5.

How did you determine it was DIMM 5 after all?

I'll also admit that I didn't read your post thoroughly and that I missed the "it always says DIMM 0" part. It looked like an easy sort of question, and I didn't take the time needed to ensure I was actually answering your question, for which I apologize.

Glenn -----OTR/L, MOT, Tx
     
bobpalmer  (op)
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Dec 7, 2009, 05:34 AM
 
The dual chip Mac Pro has 8 DIMM slots, with slots 1 - 4 on one side, and slots 5-8 on the other. The filling order is: 2 DIMM's> Slots 1 & 2; 3 DIMM's> Slots 1, 2, & 3; 4 DIMM's> Slots 1, 2, 5, & 6; 6 DIMM's> Slots 1, 2, 3, 5, 6, & 7; 8 DIMM's> All 8 slots.

The machine is configured with 8GB in 4x 2GB DIMM's. So I had memory in Slots 1, 2, 5, & 6. When the memory in slot 5 failed, the CoreServices/Memory Slot Utility.app popped up a window saying I had a non-optimal memory configuration and should move the DIMM in slot 6 to slot 3. When I took the machine in to the Apple store for service, they swapped the DIMM's in Slot 1 and 5 to determine if the problem was the DIMM or the processor assembly motherboard. The Memory Slot Utility then complained about no memory in slot 1. So they replaced the failed DIMM. System Profiler also showed that Slot 5 was empty, even though there was a DIMM in that slot. After swapping the DIMM's between slots 1 and 5, then System Profiler showed that Slot 1 was empty.

Internally, I would expect the OS to start counting at 0. Using IORegistryExplorer looking in the IODeviceTree then memory, I see the property 'slot-names' with the value: <" ", "DIMM 1", "DIMM 2", "DIMM 3", "DIMM 4", "DIMM 5", "DIMM 6", "DIMM 7", "DIMM 8">. Index 0 here is blank.

Another possibility is knowing how each DIMM maps into the hardware physical address space. The IA32_MC8_ADDR(0x422) value may be the physical address of the failing read operation, and that could point to the DIMM. Some of the addresses from various crashes are:
IA32_MC8_ADDR(0x422): 0x000000024248c6c0
IA32_MC8_ADDR(0x422): 0x00000001005ec640
IA32_MC8_ADDR(0x422): 0x000000014240c6c0
IA32_MC8_ADDR(0x422): 0x0000000105dec640
IA32_MC8_ADDR(0x422): 0x000000014052c640
IA32_MC8_ADDR(0x422): 0x0000000143dec640
But DIMM memory mapping into the physical address space may be fluid, based on how many DIMMs and the amount of memory in each DIMM.
MacPro 2x 2.93GHz Quad-Core Intel Xeon
Power Mac 4x 2.5GHz G5 (SETI #1 RAC May 4, 2006)
Power Mac 2x 1GHz G4
     
ghporter
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Dec 7, 2009, 07:49 PM
 
Very interesting. I knew that the MP banked RAM, though not the details. I think the whole "DIMM 1" thing is to make it more user friendly, though for the user population I expect the Mac Pro is aimed at, I'd think that wouldn't be needed.

And the log should have reported the correct DIMM as faulty, especially since it was being appropriately reported through the Memory Slot Utility.app. I'm very confused by that...

Glenn -----OTR/L, MOT, Tx
     
   
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