> Your best bet is to look at the various ``sunmon.h'' files scattered
> around /usr/include in SunOS (and NetBSD.)  Look for either "PROM_BASE" or
> "MON_START".

FWIW /usr/include/mon/openprom.h in SunOS4 says:

#if     defined(sun4c) || defined(sun4m)
#define MONSTART        (0xffd00000)
#define MONEND          (0xfff00000)
#endif

- Havard