Added c16/plus4 fast(), isfast() and slow() functions, and updated the documentation accordingly.

libsrc/plus4/fast.s

@@ -0,0 +1,22 @@
+;
+; Marco van den Heuvel, 2018-03-20
+;
+; void fast (void);
+; /* Switch the CPU into double clock mode. */
+;
+
+        .export         _fast
+
+        .include        "plus4.inc"
+
+
+.proc   _fast
+
+        lda     TED_CLK
+        and     #%11111101
+        sta     TED_CLK
+        rts
+
+.endproc
+
+

libsrc/plus4/isfast.s

@@ -0,0 +1,22 @@
+;
+; Marco van den Heuvel, 2018-03-20
+;
+; unsigned char isfast (void);
+; /* Returns 1 if the CPU is in double clock mode. */
+;
+
+        .export         _isfast
+
+        .include        "plus4.inc"
+
+
+.proc   _isfast
+
+        lda     TED_CLK
+        lsr
+        and     #$01
+        ldx     #$00
+        rts
+
+.endproc
+

libsrc/plus4/slow.s

@@ -0,0 +1,22 @@
+;
+; Marco van den Heuvel, 2018-03-28
+;
+; void slow (void);
+; /* Switch the CPU into single clock mode. */
+;
+
+        .export         _slow
+
+        .include        "plus4.inc"
+
+
+.proc   _slow
+
+        lda     TED_CLK
+        ora     #%00000010
+        sta     TED_CLK
+        rts
+
+.endproc
+
+