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Re: New Format For Memory " reg" Property

On May 31, 2004, at 12:16 AM, W. W. Gilpin wrote:

What is the new format used on the PowerMacG5 for the " reg" property of the "memory@0,0" entry in the IORegistry / Open Firmware? It is different from the format described in QA1065 which is used by machines prior to the G5.

My goal is to provide the same information about installed RAM DIMMs as System Profiler.

Somehow, the information below is telling me that I have a 256MB DIMM in each of slots 0 and 1, and a 512MB DIMM in each of slots 2 and 3.

00000000 00000000 20000000 00000000 00000000 00000000 00000000 20000000
20000000 00000000 40000000 20000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000

Is this information documented anywhere? My searches have proven fruitless thus far.

It's interesting to try to decode it, though. G5 physical addresses are 64 bits so we can assume that address fields will now be double the width. They may have stuck with 32-bit size fields on on the assumption (probably safe) that we won't see any DIMMs larger than 2GB soon, and if we do they won't be addressable with the current memory controller anyways. Three 32-bit words per slot seems to fit: there are eight memory slots in the G5, and the data you copied is 8 * 3 = 24 32-bit words long.

If we take the groupings to be 64 bits of address followed by 32 bits of size, we get:

00000000 00000000 20000000
00000000 00000000 00000000
00000000 20000000 20000000
00000000 40000000 20000000
00000000 00000000 00000000
00000000 00000000 00000000
00000000 00000000 00000000
00000000 00000000 00000000

or slot 0 = 512MB @ 0, slot 1 = empty, slot 2 = 512MB @ 512MB, slot 3 = 512MB @ 1GB, and the rest of the slots all empty. Obviously this is not quite right, but at least the total memory size is correct, as are slots 2 and 3, and there are no overlaps or gaps. Perhaps the two 256 MB DIMMs are being represented as a single DIMM for some reason.
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 >New Format For Memory " reg" Property (From: "W. W. Gilpin" <email@hidden>)



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