From ba0cf9e5293f258c58ced1fcc47f558e7419dae4 Mon Sep 17 00:00:00 2001 From: Miquel Sabaté Solà Date: Mon, 10 Mar 2025 22:55:41 +0100 Subject: Provide an example on multiscreen scrolling MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Signed-off-by: Miquel Sabaté Solà --- shared/asm.s | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100644 shared/asm.s (limited to 'shared/asm.s') diff --git a/shared/asm.s b/shared/asm.s new file mode 100644 index 0000000..67b195c --- /dev/null +++ b/shared/asm.s @@ -0,0 +1,22 @@ +;; Jump And Link: jump to subroutine but use the return address that the caller +;; had whenever the given subroutine runs `rts`. In other words, "link" the +;; return address from the caller to the callee. +;; +;; This is in practice the same as using `jmp` but it bears the semantic +;; connotation of the `jsr` one. That is, instead of this: +;; +;; jsr subroutine +;; rts +;; +;; It's more adviseable to do the following for better stack management: +;; +;; jmp subroutine +;; +;; That being said, the `jmp` instruction is also used in many other contexts, +;; and so sometimes it's needed to clarify that: "no, I have not messed up, +;; using `jmp` here instead of `jsr` is deliberate". Hence, instead of adding a +;; comment every time this small optimization is being done, use this +;; pseudo-instruction. +.macro JAL ADDR + jmp ADDR +.endmacro -- cgit v1.2.3