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Open Firmware device tree gives no clue what device might decode at physical address 0x80000000 to 0x8008200 on a G4 New World Macintosh. The mmu has three adjacent Virtual=Real translations for that block. They are the only address translations reported between the top or physical dram at 20000000 and the start of the PCI bridges at f0000000. The cpu node has marked them unavailable.

I now update the question because I discover the KeyLargo southbridge chip accepts addresses in that range, but I still don't know what device is at that physical address.

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migrated from Jun 16 '10 at 16:11

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I'm not a specialist in Macs, but the article powerbook G4 issues after 9.10 upgrade says:

dmesg output:
[ 35.304239] yenta_cardbus 0001:10:13.0: pcmcia: parent PCI bridge Memory window: 0x80000000 - 0xafffffff

So it might be the PCMCIA.

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is a "G4 New World Macintosh" a laptop? cause otherwise it probably wouldn't have a built-in PCMCIA device... – quack quixote Jun 16 '10 at 16:48
@quack quixote: No idea. – harrymc Jun 16 '10 at 19:18
The computer being used is an eMac desktop with no PCMCIA slots – tinkerer Jun 16 '10 at 22:59
@tinkerer: If it's a PCI slot, you might just start taking the cards out and see. But it might simply be an empty slot, so it's there but no device. – harrymc Jun 17 '10 at 5:16
Some good clues here which seem to be backed up by further investigation of Open Firmware properties, even though no definitive answer yet: cpu node confirms all address space "available" except 80000000-cfffffff (more than I originally thought!) Maybe, as comments have suggested, it is hardware supported by the rom regardless of whether the rom is installed in a suitably equipped computer or not. (The eMac has no expansion slots) See my user profile for more background on relevance of question. – tinkerer Jun 18 '10 at 2:41

Why are there only 7 hex digits in that upper address you're interested in? Did you mean
0x80008200 or did you mean
0x80082000 ?

If you meant the latter, that looks like a little over 512KB, which I believe was the size of the L2 cache in some models of the PPC 74xx (G4) processor, which could be a clue. See if you have an l2-cache node somewhere in your Open Firmware device tree, and poke around there.

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You're right, it should be 0x80082000, but according to manufacturer docs, the 7455 cpu has a 256-Kbyte "on-chip physically addressible L2 cache. I assumed "on-chip" meant it doesn't require address space outside the cpu but, if not, what could they mean by "physically addressible? – tinkerer Jun 20 '10 at 11:45
What's the Model ID of the particular eMac you're working with? I'm looking for the information you can get from System Profiler that would be in the format something like "PowerMacX,Y". – Spiff Jun 22 '10 at 4:01
eMac PowerMac4,4 PowerPC G4 (3.3) l2 Cache 265 KB – tinkerer Jun 22 '10 at 11:08
up vote 1 down vote accepted

The unidentified physical addresses are resources accessed on or via the KeyLargo Mac/IO chip:

80000000 - 8007ffff gpio (includes internal hd and cdrom)
80080000 - 80080fff usb1
80081000 - 80081fff usb0

This may be verified at the Open Firmware prompt as follows (although it could differ in some details from one eMac to the next):

dev  pci1  mem-addr-base  .
dev  usb1  hc-base  .
dev  usb0  hc-base  .
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