Re: [PATCH 6/7] mac_via: fix 60Hz VIA1 timer interval

[Laurent Vivier]

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-ayland@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...

Thanks,
Laurent