4baecec0b1
VAX 11/.750 Boot ROM code makes non-longword memory references to MassBus and Unibus register space. Minor changes were necessary to allow this behavior which was architecturally undefined behavior, but had real code which depended on it. Added a BOOTDEV option to the CPU to reflect the 4 position boot device selection switch on real VAX 11/750 hardware. The UBA750 initial state started with the UBA map registers validly mapping the first 256KB of RAM to Unibus space. Added simulated PCS/WCS memory which boot code on some operating systems (Ultrix and other BSD derived systems) automatically loaded on the VAX 11/750. PCS/WCS was also automatically loaded by the newer versions of the BOOT ROMs.
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