Initial Creativision Import

2013-12-05 11:40:44 +00:00
parent b5ed9a1eff
commit 11be575b6d
23 changed files with 956 additions and 0 deletions
--- a/libsrc/creativision/clrscr.s
+++ b/libsrc/creativision/clrscr.s
@@ -0,0 +1,41 @@
+;*
+;* clrscr
+;*
+;* NB: All screen functions assume Graphics Mode 1 in a default configuration.
+;* Therefore, this is hard coded to use $1000-$12FF as screen VRAM.
+
+    .export     _clrscr
+    .include    "creativision.inc"
+    
+_clrscr:
+
+    sei         ; Disable interrupts. Default INT handler reads VDP_STATUS
+                ; and would lose any setup done here.
+                
+    lda         #$00    ; VRAM offset low
+    sta         VDP_CONTROL_W
+    
+    lda         #$50    ; VRAM offset high ($10 OR $40)
+    sta         VDP_CONTROL_W
+    
+    lda         #$C0    ; Space from ROM setup
+    
+    ldx         #0
+    ldy         #3
+    
+L1:     sta             VDP_DATA_W
+    inx
+    bne         L1
+    dey
+    bne         L1
+    
+    cli                         ; Let interrupts go again
+    
+    lda         #0
+    sta         CURSOR_X
+    sta         CURSOR_Y
+    sta         <SCREEN_PTR
+    lda         #$10
+    sta         >SCREEN_PTR
+    
+    rts