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Awatmath.2126 net.unix-wizards utcsrgv!utzoo!decvax!watmath!dmmartindale Wed Mar 24 13:36:29 1982 Re: cp rds fault We had the same sort of symptom when our 780 was first installed. It would run fine for a few weeks, then start crashing every few hours with cp rds faults, always rebooting itself and cleaning up. I'd run the microdiagnostics and there would be no error, and the problem would promptly vanish. I eventually discovered that it was a memory board (Trendata in this case) which wasn't being initialized properly during the powerup sequence, and after a powerup every other quadword on that card had bad ECC bits. Since UNIX clears memory with a movc5 (which does longword writes) and the memory controller writes the bad data back into memory when it gets a multiple-bit ECC error on a longword write, the memory contents are still garbage after UNIX has tried clearing them. Then, as soon as the process which was allocated this memory referenced it, the RDS fault would occur (RDS (Read Data Substitute) means uncorrectable ECC error; I should have explained that earlier). We would reboot and run for several more hours before UNIX even tried to use the bad memory again, since the bad card was near the high end of the 4Mb. When I got around to running microdiagnostics, they would fix the problem; I suspect that the microdiagnostics start out by clearing memory using clrq's, which WILL overwrite the bad data in memory and fix the problem until the next power flicker. So, if you get repeated RDS faults but aren't getting any soft ECC errors on the memory and the memory diagnostics run fine, take a look at the physical address that generated the fault. If it's always on the same memory card, suspect the problem above. You should be able to verify it by exchanging this card with another one and seeing if the problem migrates. Has anyone else seen this problem?

Dave Martindale, watmath!dmmartindale

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