[uae] Re: Some Progress With the Cocoa GUI

  • From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
  • To: uae@xxxxxxxxxxxxx
  • Date: Sat, 16 Apr 2005 15:56:00 +0200 CEST

Hi Richard,

Richard Drummond <evilrich@xxxxxxxxxxxxxx> wrote:
> On Friday 15 April 2005 08:49 pm, Axel Dörfler wrote:
> > That sounds interesting. How are you going to do this?
> Well, I'm really looking at other timer APIs and even trying to guage 
> whether 
> using a plain old gettimeofday() has much of an in impact on 
> performance on 
> the various host platforms.

I would guess it's pretty low overhead on most platforms, at least it 
would be worth a try.

> OS X is easy to improve, though. The Mach kernel provides functions 
> to get the 
> PPC timebase counter and query its tick rate (thus no calibration is 
> required 
> and Mach's calibration should be more accurate anyway). I don't know 
> if 
> frequency scaling has an effect on the timebase register, however 
> (since 
> AFAIK it's not directly tied to CPU frequency, it might not).

I'm pretty sure it's not tied to the CPU frequency, so it should be a 
good candidate.

> > Under BeOS, BTW you can easily read out the frequency of CPU, but 
> > that
> > would probably help you only if you knew how fast the CPU in 
> > question
> > is, right?
> How accurate is the frequency read-out - that is, is it actually 
> measured by 
> BeOS? If it is accurate then that should be enough, since (AFAIK) the 
> TSC 
> frequency is always the same as the clock frequency (knowing the CPU 
> type 
> might help to determine the situations where it's not).

It's measured by BeOS on startup; BeOS depends its timing on the TSC 
itself (that's why it has numerous problems on CPUs that change their 
frequency). So it's as exact as BeOS' timing.

> > At least, one could remember the CPU model, and its speed, so that 
> > you
> > would only need to recalibrate if the model has changed.
> True.
> I'd actually like to find other high-resolution/low-overhead timers 
> on x86 
> platforms because of the problem that frequency-scaling has on the 
> TSC. This 
> means finding appropriate OS-specific high-resolution timer APIs.

There is probably just not that much choice in userland.

> Linux is a bit of a pain. Unfortunately I would suspect that very few 
> people 
> have a kernel built with high-resolution timer suppport. ;-)

Probably not :-)

> > (And some day, I promise, I will do the GUI integration :-))
> That's okay. I haven't had as much spare time as would like at the 
> moment, 
> either. ;-)

It's a pity :-)


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