diff options
Diffstat (limited to 'hw/misc')
| -rw-r--r-- | hw/misc/mac_via.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c index 9617e04f02..36e70674fe 100644 --- 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); |