> I would probably make a global integer flag variable:
> int mac68k_use_tt1 = 0;

I forgot the important part.  On Duo, set mac68k_use_tt1 to 1 in the
setmachdep() function.

> And then in locore.s:
> 		.globl	_mac68k_use_tt1

This should be
		GLOBAL(mac68k_use_tt1)

> 		tstl	_mac68k_use_tt1

and that should be:
		tstl	_C_LABEL(mac68k_use_tt1)

My apologies for the initial misinformation.

Think of:
		tstl	_C_LABEL(foo)
		bne	Lfoo
as:
		if (foo) goto Lfoo;

and
		tstl	_C_LABEL(foo)
		beq	Lfoo
as:
		if (!foo) goto Lfoo;

and
		bra	Lfoo
as:
		goto Lfoo;

-allen