First public commit.

lenser/a5200/viewer/awyt5200.i

@@ -0,0 +1,53 @@
+; Atari 5200 "how long to show the picture" epilogue (no OS, pure hardware).
+; Selected at assembly time by WAITMODE (set by a5200/viewer/assemble.py):
+;   0  forever       -- just loop
+;   1  until a button -- poll the keypad (POKEY) and triggers (GTIA), then reset
+;   2  WAITSECS secs  -- count frames via ANTIC VCOUNT, then reset
+; "Exit" jumps through the BIOS reset vector, which re-runs the cartridge and so
+; re-displays the picture (a cartridge console has no OS to return to).
+
+#if WAITMODE == 0
+awloop:
+        jmp awloop
+#endif
+
+#if WAITMODE == 1
+        lda #$03
+        sta $e80f               ; POKEY SKCTL -- enable keypad scanning
+awloop:
+        lda $c010               ; GTIA TRIG0 (fire button); 0 = pressed
+        and #$01
+        beq awexit
+        lda $e80f               ; POKEY SKSTAT; bit2 = 0 while a keypad key is down
+        and #$04
+        bne awloop
+awexit:
+        jmp ($fffc)             ; BIOS reset -> re-display
+#endif
+
+#if WAITMODE == 2
+        lda #<(WAITSECS*RATE)
+        sta $80
+        lda #>(WAITSECS*RATE)
+        sta $81
+awloop:
+        lda $80
+        ora $81
+        beq awexit              ; counted all the frames
+vw1:
+        lda $d40b               ; ANTIC VCOUNT
+        bne vw1                 ; wait for top of frame (VCOUNT = 0)
+vw2:
+        lda $d40b
+        beq vw2                 ; wait until it leaves the top -> one frame elapsed
+        lda $80
+        sec
+        sbc #$01
+        sta $80
+        lda $81
+        sbc #$00
+        sta $81
+        jmp awloop
+awexit:
+        jmp ($fffc)             ; BIOS reset -> re-display
+#endif