Re: [RFC 00/10] hw/mos6522: VIA timer emulation fixes and improvements

[Mark Cave-Ayland]

On 01/09/2021 08:57, Mark Cave-Ayland wrote:

> I had a quick look at your via-timer branch at 
> https://github.com/fthain/qemu/commits/via-timer and spotted that your work is based 
> upon the v6.0 release. Before digging further into this, can you try using vanilla 
> git master or the v6.1 tag instead as there are a couple of related fixes from the 
> 6.1 development cycle that you are missing:
>
> 82ff856fe7 ("mac_via: fix 60Hz VIA1 timer interval")
> - This fixed the 60Hz VIA1 timer interval (it was running 100x too fast) and so could 
> limit the virtual CPUs ability to process the 100Hz timer.
>
> 30ca7eddc4 ("mac_via: remove VIA1 timer optimisations")
> - This fixed an issue whereby constant writes to portB would reset the 60Hz VIA1 
> timer and 1Hz VIA1 timer (Probably not relevant here, but worth having).

Ah my mistake, clearly not enough caffeine this morning - looks like these patches 
did make v6.0 after all :/

I'll have a go at some basic timer measurements using your patch to see what sort of 
numbers I get for the latency here. Obviously QEMU doesn't guarantee response times 
but over 20ms does seem high.


ATB,

Mark.