kbhit() function and scrolling.

Patch provided by Jeff Tranter.

libsrc/osic1p/kbhit.s

@@ -0,0 +1,28 @@
+;
+; unsigned char kbhit (void);
+;
+
+        .export _kbhit
+        .include "osic1p.inc"
+
+_kbhit:
+        lda     #%11111110      ; Select first keyboard row
+scan:
+        sta     KBD             ; Select keyboard row
+        tax                     ; Save A
+        lda     KBD             ; Read keyboard columns
+        ora     #$01            ; Mask out lsb (Shift Lock), since we ignore it
+        cmp     #$FF            ; No keys pressed?
+        bne     keypressed
+        txa                     ; Restore A
+        sec                     ; Want to shift in ones
+        rol     a               ; Rotate row select to next bit position
+        cmp     #$FF            ; Done?
+        bne     scan            ; If not, continue
+        ldx     #$00            ; High byte of return is always zero
+        lda     #$00            ; Return false
+        rts
+keypressed:
+        ldx     #$00            ; High byte of return is always zero
+        lda     #$01            ; Return true
+        rts