Add C support for Atari 2600 (VCS)

2017-01-08 19:12:55 +01:00
parent 1fc2dfb64f
commit c1aac0de0e
13 changed files with 456 additions and 0 deletions
--- a/libsrc/atari2600/crt0.s
+++ b/libsrc/atari2600/crt0.s
@@ -0,0 +1,49 @@
+; Atari VCS 2600 startup code for cc65
+;
+; Florent Flament (contact@florentflament.com), 2017
+
+        .export         _exit
+        .export         __STARTUP__ : absolute = 1
+
+        .import         __RAM_START__, __RAM_SIZE__
+        .import         copydata
+        .import         _main
+
+        .include        "zeropage.inc"
+
+
+.segment "STARTUP"
+start:
+; Clear decimal mode
+        cld
+
+; Initialization Loop:
+; * Clears Atari 2600 whole memory (128 bytes) including BSS segment
+; * Clears TIA registers
+; * Sets system stack pointer to $ff (i.e top of zero-page)
+        ldx     #0
+        txa
+clearLoop:
+        dex
+        txs
+        pha
+        bne     clearLoop
+
+; Initialize data
+        jsr     copydata
+
+; Initialize C stack pointer
+        lda     #<(__RAM_START__ + __RAM_SIZE__)
+        ldx     #>(__RAM_START__ + __RAM_SIZE__)
+        sta     sp
+        stx     sp+1
+
+; Call main
+        jsr     _main
+_exit:  jmp     _exit
+
+
+.segment "VECTORS"
+.word   start                   ; NMI
+.word   start                   ; Reset
+.word   start                   ; IRQ