On 10/03/2021 13:24, Laurent Vivier wrote:
Le 10/03/2021 à 14:10, Laurent Vivier a écrit :
Le 10/03/2021 à 13:56, Laurent Vivier a écrit :
Le 10/03/2021 à 13:32, BALATON Zoltan a écrit :
On Wed, 10 Mar 2021, Mark Cave-Ayland wrote:
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.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
---
hw/misc/mac_via.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index f994fefa7c..c6e1552a59 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -302,8 +302,8 @@ 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) + 16630000) /
+ 16630000 * 16630000;
Can you put this magic number in a #define maybe also rewriting it in a way
that shows it
corresponds to a 60 Hz interval. (There's NANOSECONDS_PER_SECOND defined in
include/qemu/timer.h
that could be used for that, there's also SCALE_MS that might replace 1000 *
1000 elsewhere in this
file). Also NANOSECONDS_PER_SECOND / 60 is 16666666, should that value be used
here instead?
In fact, the Mac Frequency is not exactly 60 Hz, in docs we can find 60.147 Hz,
in kernel 60.15 Hz.
I Think there are several ways to compute it...
In fact, we can read:
"the vertical retrace frequency is approximately 60.15 Hz, resulting in a
period of approximately
16.63 milliseconds"
https://developer.apple.com/library/archive/documentation/mac/pdf/Processes/Vertical_Retrace_Mgr.pdf
The exact value is 16625800 ns
"Macintosh Family Hardware Reference" ISBN 0-201-19255-1
"The video interface"
p. 13-3
"[...] This means the full frame is redisplayed every 370 scan lines, or once every
166625.8 µs."
Thanks Laurent! Given that the exact precision is 6 digits I don't think it's
possible to make use of conversion macros without either making it harder to read or
reducing the precision.
I think the best solution here would be to #define VIA1_60HZ_TIMER_PERIOD_NS with a
comment containing the above reference, and use that in the period calculation. Would
that be sufficient?
ATB,
Mark.
