Make screensize() fetch the values dynamically instead of using variables

that are set on startup. This is needed to support the C128, which can switch
the screen size at runtime.


git-svn-id: svn://svn.cc65.org/cc65/trunk@2042 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/c64/c64.inc

@@ -11,7 +11,7 @@ ST   		= $90		; IEC status byte
 TIME            = $A0           ; 60 HZ clock
 FNAM_LEN	= $B7		; Length of filename
 SECADR		= $B9		; Secondary address
-DEVNUM		= $BA		; Device number     
+DEVNUM		= $BA		; Device number
 FNAM            = $BB           ; Pointer to filename
 KEY_COUNT      	= $C6		; Number of keys in input buffer
 RVS             = $C7           ; Reverse flag
@@ -43,6 +43,12 @@ IRQVec		= $0314
 BRKVec		= $0316
 NMIVec		= $0318
 
+; ---------------------------------------------------------------------------
+; Screen size
+
+XSIZE           = 40
+YSIZE           = 25
+
 ; ---------------------------------------------------------------------------
 ; I/O: VIC