From b6f712ef58631992337e99dc032e162366f0264f Mon Sep 17 00:00:00 2001
From: Christian Groessler <chris@groessler.org>
Date: Tue, 27 May 2014 01:47:37 +0200
Subject: [PATCH] not a dummy implementation anymore...

---
 libsrc/atari5200/irq.s | 47 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/libsrc/atari5200/irq.s b/libsrc/atari5200/irq.s
index 2acab1826..720113f82 100644
--- a/libsrc/atari5200/irq.s
+++ b/libsrc/atari5200/irq.s
@@ -7,8 +7,53 @@
 
         .include        "atari5200.inc"
 
-; Dummy versions for now
+; ------------------------------------------------------------------------
+
+.segment        "INIT"
 
 initirq:
+        lda     VVBLKD
+        ldx     VVBLKD+1
+        sta     IRQInd+1
+        stx     IRQInd+2
+        ldy     #<IRQStub
+        ldx     #>IRQStub
+        jmp     SETVBV
+
+; ------------------------------------------------------------------------
+
+.code
+
 doneirq:
+        ldy     IRQInd+1
+        ldx     IRQInd+2
+        ;jmp     SETVBV
+        ; fall thru
+
+; ------------------------------------------------------------------------
+; Set deferred vertical blank interrupt
+; logic copied from Atari computer ROM
+
+SETVBV: txa
+        ldx     #5
+        sta     WSYNC                   ; waste 20 CPU cycles
+@1:     dex                             ; to allow VBLANK to happen
+        bne     @1                      ; if this is line "7C"
+        sta     VVBLKD+1
+        sty     VVBLKD
         rts
+
+; ------------------------------------------------------------------------
+
+.segment        "LOWCODE"
+
+IRQStub:
+        cld                             ; Just to be sure
+        jsr     callirq                 ; Call the functions
+        jmp     IRQInd                  ; Jump to the saved IRQ vector
+
+; ------------------------------------------------------------------------
+
+.data
+
+IRQInd: jmp     $0000
-- 
2.39.5