|
From: | Mark Cave-Ayland |
Subject: | Re: [PATCH 6/7] mac_via: fix 60Hz VIA1 timer interval |
Date: | Wed, 10 Mar 2021 22:11:07 +0000 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 |
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-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...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.pdfThe 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.
[Prev in Thread] | Current Thread | [Next in Thread] |