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.
