cbm stuff from greggs pull request

libsrc/cbm/cpeekrevers.s

@@ -0,0 +1,35 @@
+;
+; 2016-02-28, Groepaz
+; 2017-06-15, Greg King
+;
+; unsigned char cpeekrevers (void);
+;
+
+        .export         _cpeekrevers
+
+; Get a system-specific file.
+; Note:  The cbm610, and c128 targets need special
+; versions that handle RAM banking and the 80-column VDC.
+
+.if     .def(__C16__)
+        .include        "plus4.inc"     ; both C16 and Plus4
+.elseif .def(__C64__)
+        .include        "c64.inc"
+.elseif .def(__CBM510__)
+        .import         CURS_X: zp, SCREEN_PTR: zp
+        .include        "cbm510.inc"
+.elseif .def(__PET__)
+        .include        "pet.inc"
+.elseif .def(__VIC20__)
+        .include        "vic20.inc"
+.endif
+
+
+_cpeekrevers:
+        ldy     CURS_X
+        lda     (SCREEN_PTR),y  ; get screen code
+        and     #$80            ; get reverse bit
+        asl     a
+        tax                     ; ldx #>$0000
+        rol     a               ; return boolean value
+        rts