* hw/misc/mos6522: What is VIA_TIMER_FREQ value?
@ 2023-02-06 16:22 Philippe Mathieu-Daudé
2023-02-06 16:25 ` Philippe Mathieu-Daudé
2023-02-06 22:14 ` Mark Cave-Ayland
0 siblings, 2 replies; 3+ messages in thread
From: Philippe Mathieu-Daudé @ 2023-02-06 16:22 UTC (permalink / raw)
To: Mark Cave-Ayland, Laurent Vivier; +Cc: QEMU Developers, BALATON Zoltan
Hi Mark & Laurent,
In commit d811d61fbc6 Mark defined VIA_TIMER_FREQ as 4700000 / 6
(783333.33) and in commit 6dca62a0000 Laurent defined it as 783360.
What is the correct value?
Could we define it once in include/hw/misc/mac_via.h or
even include/hw/misc/mos6522.h?
Thanks,
Phil.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: hw/misc/mos6522: What is VIA_TIMER_FREQ value?
2023-02-06 16:22 hw/misc/mos6522: What is VIA_TIMER_FREQ value? Philippe Mathieu-Daudé
@ 2023-02-06 16:25 ` Philippe Mathieu-Daudé
2023-02-06 22:14 ` Mark Cave-Ayland
1 sibling, 0 replies; 3+ messages in thread
From: Philippe Mathieu-Daudé @ 2023-02-06 16:25 UTC (permalink / raw)
To: Mark Cave-Ayland, Laurent Vivier
Cc: QEMU Developers, BALATON Zoltan, open list:PReP
On 6/2/23 17:22, Philippe Mathieu-Daudé wrote:
> Hi Mark & Laurent,
>
> In commit d811d61fbc6 Mark defined VIA_TIMER_FREQ as 4700000 / 6
> (783333.33) and in commit 6dca62a0000 Laurent defined it as 783360.
Also 4700000 / 6 in hw/misc/macio/cuda.c (commit 267002cd28).
> What is the correct value?
>
> Could we define it once in include/hw/misc/mac_via.h or
> even include/hw/misc/mos6522.h?
>
> Thanks,
>
> Phil.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: hw/misc/mos6522: What is VIA_TIMER_FREQ value?
2023-02-06 16:22 hw/misc/mos6522: What is VIA_TIMER_FREQ value? Philippe Mathieu-Daudé
2023-02-06 16:25 ` Philippe Mathieu-Daudé
@ 2023-02-06 22:14 ` Mark Cave-Ayland
1 sibling, 0 replies; 3+ messages in thread
From: Mark Cave-Ayland @ 2023-02-06 22:14 UTC (permalink / raw)
To: Philippe Mathieu-Daudé, Laurent Vivier
Cc: QEMU Developers, BALATON Zoltan
On 06/02/2023 16:22, Philippe Mathieu-Daudé wrote:
> Hi Mark & Laurent,
>
> In commit d811d61fbc6 Mark defined VIA_TIMER_FREQ as 4700000 / 6
> (783333.33) and in commit 6dca62a0000 Laurent defined it as 783360.
>
> What is the correct value?
>
> Could we define it once in include/hw/misc/mac_via.h or
> even include/hw/misc/mos6522.h?
>
> Thanks,
>
> Phil.
Hi Phil,
The 6522 VIA has a 16-bit counter which is driven by an external clock crystal which
is set to 783kHz for Macs. Commit 6dca62a0000 is the correct value since that was
given in the Macintosh hardware documentation, and needs to be accurate since it was
used for timing in older Macs. The value in commit d811d61fbc6 came from Ben, and it
may be that this is how it is implemented on real PMU hardware by dividing a 4.7MHz
clock for compatibility purposes: certainly newer Macs have a much more accurate
hardware timer that would be used by the OS instead.
ATB,
Mark.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-02-06 16:22 hw/misc/mos6522: What is VIA_TIMER_FREQ value? Philippe Mathieu-Daudé
2023-02-06 16:25 ` Philippe Mathieu-Daudé
2023-02-06 22:14 ` Mark Cave-Ayland
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