Create local stack frame

NAME
	LINK -- Create local stack frame

SYNOPSIS
	LINK	An,#<data>

	Size = (Word)
	Size = (Word, Long)		(68020+)

FUNCTION
	This instruction saves the specified address register onto
	the stack, then places the new stack pointer in that register. It
	then adds the specificed immediate data to the stack pointer. To
	allocate space on the stack for a local data area, a negative value
	should be used for the second operand.

	The use of a local stack frame is critically important to the
	programmer who wishes to write re-entrant or recursive functions.
	The creation of a local stack frame on the MC680x0 family is done
	through the use of the LINK and UNLK instructions. The LINK
	instruction saves the frame pointer onto the stack, and places a
	pointer to the new stack frame in it. The UNLK instruction
	restores the old stack frame. For example:

		link	a5,#-8		; a5 is chosen to be the frame
					; pointer. 8 bytes of local stack
					; frame are allocated.
		...
		unlk	a5		; a5, the old frame pointer, and the
					; old SP are restored.

	Since the LINK and UNLK instructions maintain both the frame pointer
	and the stack pointer, the following code segment is perfectly
	legal:

		link	a5,#-4

		movem.l	d0-a4,-(sp)
		pea	(500).w
		move.l	d2,-(sp)
		bsr.b	Routine

		unlk	a5
		rts

FORMAT
	For Word size:
	~~~~~~~~~~~~~
	-----------------------------------------------------------------
	|15 |14 |13 |12 |11 |10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
	|---|---|---|---|---|---|---|---|---|---|---|---|---|-----------|
	| 0 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | REGISTER  |
	|---------------------------------------------------------------|
	|                        16 BITS OFFSET (d)                     |
	-----------------------------------------------------------------

	For Long size:
	~~~~~~~~~~~~~
	-----------------------------------------------------------------
	|15 |14 |13 |12 |11 |10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
	|---|---|---|---|---|---|---|---|---|---|---|---|---|-----------|
	| 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | REGISTER  |
	|---------------------------------------------------------------|
	|          32 BITS OFFSET (d) (16 bits of lower weight)         |
	|---------------------------------------------------------------|
	|          32 BITS OFFSET (d) (16 bits of upper weight)         |
	-----------------------------------------------------------------

	"REGISTER" indicates the number of address register.
	OFFSET is a signed value, generally negative, which enables to move
	the stack pointer.

RESULT
	None.

SEE ALSO
	UNLK