VMEbus Mapping Example
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0000 on the PCI Local bus. Thus, to translate an inbound address of 1000
0000 (the configured VMEbus Base address of this board to 8000 0000,
which is presented to DRAM as 0000 0000 and translation value of 7000
0000 is selected: 1000 0000 + 7000 0000 => 8000 0000 on the PCI Local
Bus that becomes 0000 0000 on the PowerPC bus.
5100 PCI Slave Translate
In the CHRP memory map, PCI Memory Space is based at 8000 0000.
Once again, the first 1MB is reserved for other PCI devices requiring
memory space so the Universe is configured to claim addresses from 810 0
0000 to A000 0000 that appear on the PCI Local Bus. Because this is a
CHRP memory map, the address presented on the PCI Local Bus is not
translated, so a PPC generated address of 8100 0000 appears on the PCI
Local Bus as 8100 0000. Again, the same translation calculation is
required to adjust this address to be presented as 0000 0000 on the
VMEbus. In this case, the value is 7F00 0000: 8100 0000 + 7F00 0000 =>
1 0000 0000.
5100 VME Slave Translation
In the CHRP memory map, DRAM is located at 0000 0000 on the PCI
Local Bus. As configured, the Universe accepts VMEbus addresses
between 1400 0000 and 17FF FFFF. To translate a VMEbus address of
1400 0000 to 0000 0000 on the PCI Local Bus a translation offset of EC00
0000 is chosen: 1400 0000 +EC00 0000 => 1 0000 0000. Once again, the
overflow results in the desired value.