Re: [hatari-devel] TT mono mode Timer-C problem

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

On 16/12/2011 22:50, Roger Burrows wrote:
> I was testing EmuTOS using TT mono mode (TT High), and had problems opening a
> drive window by double-clicking on the desktop icon.  After a bit of work, I
> discovered that the 200Hz (5 msec) system timer is actually running at about
> 400Hz, which (among other things), speeds up the timer interrupt at etv_timer,
> and causes double-clicks to seem twice as slow as they really are.
>
> The attached program (compiled under Lattice C on a real TT) uses the system
> ticks value in low memory to count off seconds and display them.  If you run
> this in TT mono mode, the seconds go by at about twice the normal rate.  The
> program also uses a crude loop counter to see if there is any significant
> variability in the time between clock pulses (I wondered if perhaps two clock
> pulses were being signalled every 5msec), but there doesn't seem to be.
>
> This problem occurs with either EmuTOS or TOS 3.06, but ONLY in TT mono mode.
> It does not occur if the screen mode is set to RGB.
>
> Roger Burrows

Hello

yes, it's a known limitation that at the moment the interrupt events are 
expecting the cpu clock to be 8 MHz. If you use 16 or 32 MHz, interrupts 
won't be good.
This will be fixed some day, as it can also impact falcon mode, but for 
now all the interrupts events are "locked" to the cpu freq (instead of 
the master bus freq on a real ST/TT/Falcon)

I will take a look, it should be possible to add a patch that improve 
this without too much damages.
Are you using the devel version with mercurial ?

Nicolas