1 files changed, 62 insertions, 0 deletions
diff --git a/src/crt0.s b/src/crt0.s
new file mode 100644
index 0000000..6ffb2ce
--- /dev/null
+++ b/src/crt0.s
@@ -0,0 +1,62 @@
+;
+; Startup code for cc65 (ATARI version)
+;
+; Contributing authors:
+;       Mark Keates
+;       Freddy Offenga
+;       Christian Groessler
+;       Stefan Haubenthal
+;
+
+; Hacked up, trimmed down version for fnchat.
+
+        .export         __STARTUP__ : absolute = 1      ; Mark as startup
+        .export         _exit, start
+
+        .import         _main, zerobss
+        .import         __RESERVED_MEMORY__
+        .import         __MAIN_START__, __MAIN_SIZE__
+        .import         __LOWCODE_RUN__, __LOWCODE_SIZE__
+        .include        "zeropage.inc"
+        .include        "atari.inc"
+
+; ------------------------------------------------------------------------
+
+.segment        "STARTUP"
+ _exit = WARMSV ; nothing should be calling exit() anyway.
+
+        rts     ; fix for SpartaDOS / OS/A+
+                ; They first call the entry point from AUTOSTRT; and
+                ; then, the load address (this rts here).
+                ; We point AUTOSTRT directly after the rts.
+
+; Real entry point:
+
+start:
+
+; Clear the BSS data.
+        jsr     zerobss
+
+; Set up the stack
+        lda MEMTOP
+        sta sp
+        lda MEMTOP+1
+        sta sp+1
+
+; Set the keyboard to upper-/lower-case mode.
+        ldy     #0
+        sty     SHFLOK
+        dey                     ; Set Y to $FF
+        sty     CH              ; remove keypress which might be in the input buffer
+
+; Go directly to main(). No support for CLI arguments, no saving
+; any machine state for a clean exit, because we don't exit.
+       jmp _main
+
+; ------------------------------------------------------------------------
+
+.segment "LOWCODE"       ; have at least one (empty) segment of LOWCODE, so that the next line works even if the program doesn't make use of this segment
+.assert (__LOWCODE_RUN__ + __LOWCODE_SIZE__ <= $4000 || __LOWCODE_RUN__ > $7FFF || __LOWCODE_SIZE__ = 0), warning, "'lowcode area' reaches into $4000..$7FFF bank memory window"
+; check for LOWBSS_SIZE = 0 not needed since the only file which uses LOWBSS (irq.s) also uses LOWCODE
+; check for LOWCODE_RUN > $7FFF is mostly for cartridges, where this segment is loaded high (into cart ROM)
+; there is a small chance that if the user loads the program really high, LOWCODE is above $7FFF, but LOWBSS is below -- no warning emitted in this case