REG(FLAGS)          // see FLAG_* consts in isa/isa.h
REG(FLAGS_SAVED)    // see FLAG_* consts in isa/isa.h
REG(HALTED)
REG(TT_BITS)        // see TT[IO]_* consts in isa/isa.h
REG(TT_FLAGS)       // see TTF_* consts in isa/isa.h
