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Battery-Backed RAM: problems with dead battery?
#1
I inherited a system based on Turbo PMAC2 PCI Ultralite that has been running with little trouble for years. Unbeknownst to me, the system has the battery-backed RAM option (16B, I believe) and we use I46=1 to keep the P-variables in BBRAM.

The system has been operational for well over 5 years and to my knowledge the battery has never been changed so I expect it is dead. And therefore the contents of the P-variables will be garbage at boot-up.

What I'm wondering is: can this possibly cause corruption after writing good data to a P-variable? For example, suppose I say P101 = 33; is it possible that a later read from P101 will be corrupted due to the dead battery?

Thanks,
-Steve
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#2
Hi,

I am not completely sure, so I have been trying to find a PMAC with the BBRAM option (and no battery) to test this.

In the mean time, are you able to connect to your PMAC? If so, can you try writing to a BBRAM location, and see if you can read the same information back?

Below are the batterybacked memory locations:

Code:
X/Y:$050000 - $053FFF Standard BBRAM Option (32k x 24 mapped as 16k x 48)
X/Y:$050000 - $05FFFF Extended BBRAM Option (128k x 24 mapped as 64k x 48)
L:$050000 - $051FFF Alternate location for P0 – P8191 (when I46 = 1 or 3)
L:$052000 - $053FFF Alternate location for Q0 – Q8191 (when I46 = 2 or 3)

You can try it with an M-Variable like M1000->X:$50000,0,24,S

Then write M1000=10 and see if you can read it back.
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#3
(06-18-2015, 03:43 PM)CharlesP Wrote: In the mean time, are you able to connect to your PMAC? If so, can you try writing to a BBRAM location, and see if you can read the same information back?

Thanks, Charles. I didn't try exactly your test, but what we did is overwrite the problematic P-variables with valid data. The system began to function normally again, so I believe that reading does work. At least most of the time. What I was really trying to ask is whether we can rely on this or whether it may flake out occasionally.

I am going to recommend replacing the battery to avoid future problems, but was just worried about the interim.
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#4
(06-19-2015, 06:59 AM)smr99 Wrote: I am going to recommend replacing the battery to avoid future problems ...

On the topic of replacing the battery: I looked at the Turbo PMAC User, Hardware, and Software Reference Manuals for information on the type of battery and how to replace it. All I could find is: "The battery is located at component BT1." Are more details available somewhere?

I am not physically on-site, so I can't check: If we open the computer is it easy enough to find the battery? Does the battery have sufficient markings to find its part number for replacement?
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#5
Yes - the battery is near the CPU section of all PMACs.
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