AVR assembly macros for making register safe call on stack functions

function.asm

; global registers:
;	r0		- no man's land
;	r1		- return address
;	X (r26,r27)	- frame pointer

;function frame:
;---------------------------
;	return address
;	arg0
;	...
;	argn
;---------------------------
;	parent frame pointer


; for accessing the stack pointer
.equ	SPH	= 0x5E
.equ	SPL	= 0x5D


;call before loading args onto stack
	.macro func_start_args
		; save FP
		push r26
		push r27

		; new FP
		lds r26, SPL
		lds r27, SPH
	.endmacro

; load arguments
	.macro fun_arg
		push @0
	.endmacro
	.macro fun_arg_i
		pushi @0
	.endmacro
	.macro fun_arg_16
		push16 @0, @1
	.endmacro
	.macro fun_arg_16_i
		push16i @0
	.endmacro

; get args (does not remove from stack)
	.macro arg_get
		push @0
		lpm @0, X+
	.endmacro
	.macro arg_get16
		push @0
		push @1
		
		lpm @0, X+
		lpm @1, X+
	.endmacro

; unload args (call before returning for every arg)
	.macro arg_unload
		pop r0
		pop r0
	.endmacro
	.macro arg_unload16
		pop r0
		pop r0
		pop r0
		pop r0
	.endmacro

; call function
	.macro func_call
		call @0

		; restore FP
		pop r27
		pop r26
	.endmacro


; place at entry of function
	.macro func_ent
		pop r1 ; keep ret address for later
	.endmacro

; place at exit of function
	.macro func_ret
		push r1 ; restore ret address
		ret
	.endmacro