First public commit.

lenser/viewer/wait.i

@@ -0,0 +1,77 @@
+; Shared "how long to show the picture" epilogue for the simple C64 viewers.
+; Selected at assembly time by WAITMODE (set by viewer/assemble.py):
+;   0  forever       -- never returns; the picture stays until reset
+;   1  until a key   -- jsr GETIN until a key is pressed, then fall through
+;   2  WAITSECS secs  -- count KERNAL jiffies (JIFFYPS per second), then fall through
+;   3  key OR secs   -- whichever comes first (keys still work, but it auto-
+;                       advances after WAITSECS); used by the slideshow viewer
+; On fall-through the caller restores the text screen and RTSes to BASIC.
+; The KERNAL IRQ is left running by these viewers, so GETIN and the jiffy clock
+; ($a0-$a2, big-endian, $a2 = least significant) both work.
+
+cv_t0 = $fb                       ; 16-bit jiffy snapshot (free after the copy)
+cv_el = $fd                       ; 16-bit elapsed jiffies
+
+#if WAITMODE == 0
+cv_wait:
+        jmp cv_wait
+#endif
+
+#if WAITMODE == 1
+        lda #$00
+        sta $c6                   ; empty the keyboard buffer first, so a key left
+                                  ; over from RUN doesn't dismiss the picture at once
+cv_wait:
+        jsr $ffe4                 ; GETIN
+        beq cv_wait
+#endif
+
+#if WAITMODE == 2
+        lda $a2
+        sta cv_t0
+        lda $a1
+        sta cv_t0+1
+cv_wait:
+        sec
+        lda $a2
+        sbc cv_t0
+        sta cv_el
+        lda $a1
+        sbc cv_t0+1
+        sta cv_el+1
+        lda cv_el+1
+        cmp #>(WAITSECS*JIFFYPS)
+        bcc cv_wait
+        bne cv_done
+        lda cv_el
+        cmp #<(WAITSECS*JIFFYPS)
+        bcc cv_wait
+cv_done:
+#endif
+
+#if WAITMODE == 3
+        lda #$00
+        sta $c6                   ; empty the keyboard buffer first
+        lda $a2
+        sta cv_t0
+        lda $a1
+        sta cv_t0+1
+cv_wait:
+        jsr $ffe4                 ; GETIN -- any key ends the slide immediately
+        bne cv_done
+        sec                       ; else check the elapsed-jiffies timeout
+        lda $a2
+        sbc cv_t0
+        sta cv_el
+        lda $a1
+        sbc cv_t0+1
+        sta cv_el+1
+        lda cv_el+1
+        cmp #>(WAITSECS*JIFFYPS)
+        bcc cv_wait
+        bne cv_done
+        lda cv_el
+        cmp #<(WAITSECS*JIFFYPS)
+        bcc cv_wait
+cv_done:
+#endif