Memory space conflicts
NetBSD maps memory on Cardbus and PCMCIA cards in order to access the cards (including reading CIS tuples on PCMCIA cards) and access the devices using the RBUS abstraction. When the mapping does not work, PCMCIA cards are typically ignored on insert, and Cardbus cards are recognized but nonfunctional. On i386, the kernel has a heuristic to choose a memory address for mapping, defaulting to 1 GB, but choosing 0.5 GB on machines with less than 192 MB RAM and 2 GB on machines with more than 1 GB of RAM. The intent is to use an address that is larger than available RAM, but low enough to work; some systems seem to have trouble with addresses requiring more than 20 address lines. On i386, the following kernel configuration line disables the heuristics and forces Cardbus memory space to be mapped at 512M; this value makes Cardbus support (including PCMCIA attachment under a cbb) work on some notebook models, including the IBM Thinkpad 600E (2645-4AU) and the Compaq ARMADA M700:
options RBUS_MIN_START="0x20000000"