- out __SP_L__,r28
- out __SREG__,__tmp_reg__
- out __SP_H__,r29
-
- A `-mcall-prologues' prologue look like this:
- ldi r26,<LOCALS_SIZE>
- ldi r27,<LOCALS_SIZE>/265
- ldi r30,pm_lo8(.L_foo_body)
- ldi r31,pm_hi8(.L_foo_body)
- rjmp __prologue_saves__+RRR
- .L_foo_body: */
+ out __SP_H__,r29
+ out __SREG__,__tmp_reg__
+ out __SP_L__,r28
+
+ A typical AVR function prologue without a frame pointer might look like
+ this:
+ push rXX ; saved regs
+ ...
+
+ A main function prologue looks like this:
+ ldi r28,lo8(<RAM_ADDR> - <LOCALS_SIZE>)
+ ldi r29,hi8(<RAM_ADDR> - <LOCALS_SIZE>)
+ out __SP_H__,r29
+ out __SP_L__,r28
+
+ A signal handler prologue looks like this:
+ push __zero_reg__
+ push __tmp_reg__
+ in __tmp_reg__, __SREG__
+ push __tmp_reg__
+ clr __zero_reg__
+ push rXX ; save registers r18:r27, r30:r31
+ ...
+ push r28 ; save frame pointer
+ push r29
+ in r28, __SP_L__
+ in r29, __SP_H__
+ sbiw r28, <LOCALS_SIZE>
+ out __SP_H__, r29
+ out __SP_L__, r28
+
+ A interrupt handler prologue looks like this:
+ sei
+ push __zero_reg__
+ push __tmp_reg__
+ in __tmp_reg__, __SREG__
+ push __tmp_reg__
+ clr __zero_reg__
+ push rXX ; save registers r18:r27, r30:r31
+ ...
+ push r28 ; save frame pointer
+ push r29
+ in r28, __SP_L__
+ in r29, __SP_H__
+ sbiw r28, <LOCALS_SIZE>
+ cli
+ out __SP_H__, r29
+ sei
+ out __SP_L__, r28
+
+ A `-mcall-prologues' prologue looks like this (Note that the megas use a
+ jmp instead of a rjmp, thus the prologue is one word larger since jmp is a
+ 32 bit insn and rjmp is a 16 bit insn):
+ ldi r26,lo8(<LOCALS_SIZE>)
+ ldi r27,hi8(<LOCALS_SIZE>)
+ ldi r30,pm_lo8(.L_foo_body)
+ ldi r31,pm_hi8(.L_foo_body)
+ rjmp __prologue_saves__+RRR
+ .L_foo_body: */