Day 11 - The JSR Instruction

JSR?

	
	JSR stands for Jump to SubRoutine and is used to, well... jump to a subroutine.

How do we use it?

	We use it by giving it the name of the label that we want to jump to.
Example:

	jsr OurSub
	; blah, some code

OurSub:
	; blah, some more code
	; return to instruction after the JSR.

Return? How?

	With the RTS (ReTurn from Subroutine) instruction of course! So the full
version of the above stuff is:

	jsr OurSub
	; blah, some code

OurSub:
	; blah, some code
	rts  ; returns and resumes execution at the first "blah, some code".

Something more

	One thing to remember though, if you just want to separate your code out.
then what is described above should be enough. If you want to jump to a subroutine based
on a comparison, you would have to do something like the following:

	cmp #5  ; compare A with 5
	bne DONTcall ; if A isn't 5 we branch over the subroutine call.
	jsr OurSub
DONTcall:



	;somewhere... possibly far away:
OurSub:

	;blah, code.
	rts ; return

This Day In Review

	I hope you get that, if you don't.. well.. I just won't think like that. ;)
Seriously though, if you ever need help with something from these tutorials or find
an error, don't hesitate to tell me.
	
	Happy coding!,
		-Mike H a.k.a GbaGuy

Intro - Day 12