Hello,

if I create a game that works only in 50 hertz, does this mean that this game cannot be played in Asia/USA?
(or do they have the ability to play at 50 hertz as well ??)

If you set the VDP to 50Hz, the game will run. If people want to see it, they need a TV or monitor which can handle 50Hz signals. Most can.

Can I conclude that back in the 80's & 90's asiatic, american (and maybe eastern europeans) didnt have 50 hertz monitors/tv's ???

Yes you can... and basically they still don't, just like we basically don't have 60Hz tv's. Read more about it here and here.

The basic strategy to make your game work on all MSX machines is to not touch the interrupt frequency

If however, you do want to have full control over the speed of your game, I would suggest the following:

• Test bit 7 of the ID byte at address #0028 of the MSX BIOS. This tells you which interrupt frequency is used:
  0 - 60Hz
  1 - 50Hz
  
• Optionally set the VDP to the frequency just read (just in case some other program flipped it
  
• In your interrupt routie do something like:
  

  IF interrupt fq = 60Hz
  THEN counter = counter - 1
       IF counter = 0
       THEN counter = 6: RETURN ' Yes, abort interrupt routine!
       ENDIF
  ENDIF
  do interrupt stuff
  

In this way you'll skip 1 out of 6 interrupts when running at 60Hz, effectively making the game run at 50Hz. And then you can even give the user the option to run the game at either 50 or 60 Hz...

Yeah that will work great in a smooth scrolling game. However on music the effect is less disturbing.
I get the feeling SM2 is too heavy to run under 60Hz (I really don't know why ).

stangely the difference between 50 and 60 hertz is big.
at 50 hertz:
With the maximum amount of enemies in play the game almost runs at full framespeed 50 frames per second.
With less enemies in play the game runs very fluently (50 frames per second)

When the game runs at 60 hertz, AND there are more then 3 enemies in play the game starts to slow down (20/30 frames per second).

It is not stange, you lose 20% of cpu power wich is a lot. Same for the vdp (allmost 1kb less).
Is the music player already implemented?

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Yeah that will work great in a smooth scrolling game.

Would you really notice the difference between running at 5/6 of 60Hz or at full on 50Hz? I strongly doubt it...

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Would you really notice the difference between running at 5/6 of 60Hz or at full on 50Hz? I strongly doubt it...

You definitely will notice it, since you will skip one whole interrupt. Where 'normally' in 60Hz the interrupts occur 6 times and you once skip one without equally spreading the extra time per interrupt, you'll get a nasty glitch. With music you can't hear the difference, except if you really carefully listen to it (though that might be my imagination), I don't exactly know why. With scrolls however, you can very clearly see the glitch in it!

Games run much faster at 60Hz with no doubt.

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With scrolls however, you can very clearly see the glitch in it!

Well, then there's only one solution: 10Hz framerate (the largest common divisor of 50 and 60)

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It is not stange, you lose 20% of cpu power wich is a lot. Same for the vdp (allmost 1kb less). Is the music player already implemented?

yes, why?

That is good to know, why, so you won't run into more surprises.

I've been writing a couple of demoparts the last year (e.g. MSX Unleashed) and I must say that there is indeed a waste of cpu resources when doing something that works in both 50 and 60 hz. Most animations needs to be adapted to be flicker free in 60Hz which means that you loose 20% CPU time (as already stated). And 20% is quite a lot. For the music its easy though since most music doesn't sound much differennce if made for 50Hz and then in 60Hz you just skip every 6th update.