On 04/16/2015 02:39 AM, Mario Kleiner wrote: > On 04/16/2015 03:29 AM, Peter Hurley wrote: >> On 04/15/2015 05:26 PM, Mario Kleiner wrote:
>> Because the time scales for these events don't require that level of >> resolution; consider how much code has to get executed between a >> hardware vblank irq triggering and the vblank counter being updated. >> >> Realistically, the only relevant requirement is that the timestamp >> match the counter. >> > > Yes that is the really important part. A msec delay would possibly matter for > some timing sensitive apps like mine - some more exotic displays run at 200 > Hz, and some apps need to synchronize to the vblank not strictly for > graphics. But i assume potential delays here are more on the order of a few > microseconds if some pending loads from the cache would get reordered for > overall efficiency? I'd be surprised if the delay were as much as 1 us. The latency to return to userspace significantly dwarfs any observable effects having missed the vblank count update by 1 instruction. Regards, Peter Hurley
