mac_via: fix 60Hz VIA1 timer interval

The 60Hz timer is initialised using timer_new_ns() meaning that the timer
interval should be measured in ns, and therefore its period is a thousand
times too short.

Use a define for the 60Hz timer period taking the more precise value as
documented in the Guide To The Macintosh Family Hardware.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <20210311100505.22596-7-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index 9617e04f02efb1d8125e071acc820549ec9c83ad..36e70674feda44d465e3f3642d8eaef4135459a9 100644 (file)
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -279,6 +279,12 @@
 #define VIA_TIMER_FREQ (783360)
 #define VIA_ADB_POLL_FREQ 50 /* XXX: not real */
 
+/*
+ * Guide to the Macintosh Family Hardware ch. 12 "Displays" p. 401 gives the
+ * precise 60Hz interrupt frequency as ~60.15Hz with a period of 16625.8 us
+ */
+#define VIA_60HZ_TIMER_PERIOD_NS   16625800
+
 /* VIA returns time offset from Jan 1, 1904, not 1970 */
 #define RTC_OFFSET 2082844800
 
@@ -302,8 +308,9 @@ static void via1_sixty_hz_update(MOS6522Q800VIA1State *v1s)
     MOS6522State *s = MOS6522(v1s);
 
     /* 60 Hz irq */
-    v1s->next_sixty_hz = (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + 16630) /
-                          16630 * 16630;
+    v1s->next_sixty_hz = (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
+                          VIA_60HZ_TIMER_PERIOD_NS) /
+                          VIA_60HZ_TIMER_PERIOD_NS * VIA_60HZ_TIMER_PERIOD_NS;
 
     if (s->ier & VIA1_IRQ_60HZ) {
         timer_mod(v1s->sixty_hz_timer, v1s->next_sixty_hz);