Implemented some CONIO peek functions.

Please refer to https://github.com/cc65/cc65/pull/532 for background info.

I wrote in https://sourceforge.net/p/cc65/mailman/message/35873183/

===
cputs() wraps to the next line if the strings is too long to fit in the current line. I don't know if it's worth the effort to allow cpeeks() to continue reading from the next line. I'd like to discuss this aspect with the actual implementers.
===

This is still as unclear today as it was when I wrote the above. Therefore this change just doesn't add cpeeks() at all.

Since f8c6c58373 the Apple II CONIO implementation doesn't "need" revers() anymore - meaning that (nearly) every possible value can be placed in VRAM with a straight cputc() (without the need for a previous revers(1)).

The implementation of cpeekc() leverages that cputc() ability by always returning the value that can be fed into cputc() without a previous revers(1). Accordingly, cpeekrevers() always returns 0.

So after the sequence revers(1); cputc(x); a cpeekc() will return a value different from x! However, I don't see this behavior braking the cpeekc() contract. I see the cpeekc() contract being defined by the sequence textcolor(cpeekcolor()); revers(cpeekrevers()); cputc(cpeekc()); placing the very same value in VRAM that there was before. And that contract is fulfilled.

include/apple2.h

@@ -207,6 +207,8 @@ void rebootafterexit (void);
 #define _textcolor(color)       COLOR_WHITE
 #define _bgcolor(color)         COLOR_BLACK
 #define _bordercolor(color)     COLOR_BLACK
+#define _cpeekcolor()           COLOR_WHITE
+#define _cpeekrevers()          0
 
 
 

include/conio.h

@@ -201,16 +201,19 @@ void __fastcall__ cputhex16 (unsigned val);
 */
 
 #ifdef _textcolor
-#  define textcolor(x)          _textcolor(x)
+#  define textcolor(color)      _textcolor(color)
 #endif
 #ifdef _bgcolor
-#  define bgcolor(x)            _bgcolor(x)
+#  define bgcolor(color)        _bgcolor(color)
 #endif
 #ifdef _bordercolor
-#  define bordercolor(x)        _bordercolor(x)
+#  define bordercolor(color)    _bordercolor(color)
 #endif
 #ifdef _cpeekcolor
-#  define cpeekcolor(x)         _cpeekcolor(x)
+#  define cpeekcolor()          _cpeekcolor()
+#endif
+#ifdef _cpeekrevers
+#  define cpeekrevers()         _cpeekrevers()
 #endif
 
 

libsrc/apple2/cpeekc.s

@@ -0,0 +1,28 @@
+;
+; 2020-07-12, Oliver Schmidt
+;
+; char cpeekc (void);
+;
+
+        .export         _cpeekc
+
+        .include        "apple2.inc"
+
+_cpeekc:
+        ldy     CH
+        .ifdef  __APPLE2ENH__
+        bit     RD80VID         ; In 80 column mode?
+        bpl     peek            ; No, just go ahead
+        tya
+        lsr                     ; Div by 2
+        tay
+        bcs     peek            ; Odd cols are in main memory
+        bit     HISCR           ; Assume SET80COL
+        .endif
+peek:   lda     (BASL),Y        ; Get character
+        .ifdef  __APPLE2ENH__
+        bit     LOWSCR          ; Doesn't hurt in 40 column mode
+        .endif
+        eor     #$80            ; Invert high bit
+        ldx     #$00
+        rts