SCREEN_PTR does only contain the offset apparently (unlike on other cbm systems), so we need extra handling

2025-06-25 05:13:09 +02:00
parent 955c6627c0
commit 4db5ac6c14
13 changed files with 356 additions and 36 deletions
--- a/libsrc/mega65/cpeekc.s
+++ b/libsrc/mega65/cpeekc.s
@@ -0,0 +1,45 @@
+;
+; 2016-02-28, Groepaz
+; 2017-06-22, Greg King
+;
+; char cpeekc (void);
+;
+
+        .include        "mega65.inc"
+
+        .export         _cpeekc
+        .importzp       ptr1
+
+_cpeekc:
+        lda     SCREEN_PTR + 1
+        clc
+        adc     #>$0800
+        sta     ptr1 + 1
+        lda     SCREEN_PTR
+        sta     ptr1
+
+        ldy     CURS_X
+        lda     (ptr1),y  ; get screen code
+        ldx     #>$0000
+        and     #<~$80          ; remove reverse bit
+
+; Convert the screen code into a PetSCII code.
+; $00 - $1F: +$40
+; $20 - $3F
+; $40 - $5f: +$20
+; $60 - $7F: +$40
+
+        cmp     #$20
+        bcs     @sk1            ;(bge)
+        ora     #$40
+        rts
+
+@sk1:   cmp     #$40
+        bcc     @end            ;(blt)
+        cmp     #$60
+        bcc     @sk2            ;(blt)
+        ;sec
+        adc     #$20 - $01
+@sk2:   ;clc                    ; both above cmp and adc clear carry flag
+        adc     #$20
+@end:   rts