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CRT in extreme slow motion
http://forums.nesdev.com/viewtopic.php?f=5&t=16957
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Author:  dougeff [ Fri Jan 19, 2018 7:40 am ]
Post subject:  CRT in extreme slow motion

I saw this on reddit retrogaming.

They play SMB with a super slow motion camera. The NES relevant video is between 1 and 4 minutes.

https://youtu.be/3BJU2drrtCM

Author:  lidnariq [ Fri Jan 19, 2018 12:05 pm ]
Post subject:  Re: CRT in extreme slow motion

I thought it a little amusing that at the peak 380kfps, there's roughly about one instruction completing for each recorded frame.

Author:  Dwedit [ Fri Jan 19, 2018 11:54 pm ]
Post subject:  Re: CRT in extreme slow motion

And here we see the 1 frame of input lag inherent to almost all NES games.

Author:  zeroone [ Mon Jan 22, 2018 2:59 pm ]
Post subject:  Re: CRT in extreme slow motion

Dwedit wrote:
And here we see the 1 frame of input lag inherent to almost all NES games.


Really? Can you elaborate?

Author:  mikejmoffitt [ Mon Jan 22, 2018 3:12 pm ]
Post subject:  Re: CRT in extreme slow motion

Dwedit wrote:
And here we see the 1 frame of input lag inherent to almost all NES games.


This depends on what you call a frame of lag. I don't think it's reasonable to poll for inputs in any game until an entire frame has been rendered; i.e. during vblank. Even modern displays still scan like the CRT does, and nothing here is intrinsic to NES games.

If you're polling inputs to process the logic for frame [n+1] at the end of frame [n], I would consider this zero frames of lag.

Author:  Dwedit [ Mon Jan 22, 2018 5:16 pm ]
Post subject:  Re: CRT in extreme slow motion

NES games run the game logic during render time. So when the pixels are rendered, you get the game state of the last frame. So all NES games have a minimum of 1 frame of lag between your input and the output being reflected on the screen.
Compare this with the Atari 2600 - Games for that system run the game logic during vblank time, and the game races the beam to render the screen. No possible input lag at all.

NES Emulators could be made to compensate for the 1 frame of internal input lag by using time travel (savestates), but I don't know of any NES emulators that do this. I have seen Genesis emulators do this though.

Author:  Kasumi [ Tue Jan 23, 2018 12:12 am ]
Post subject:  Re: CRT in extreme slow motion

I'm toyed with the idea of making a <1800 cycle thing in the vblank, then DMAing to get rid of the lag, for no other reason than just because.

Author:  JRoatch [ Tue Jan 23, 2018 8:00 am ]
Post subject:  Re: CRT in extreme slow motion

For what it's worth, my Simple button logger tool runs all logic and graphical updates within vblank.
The soon to be manufactured Action 53 volume 3 has the most up to date version of it.

Author:  psycopathicteen [ Tue Jan 23, 2018 3:25 pm ]
Post subject:  Re: CRT in extreme slow motion

Wow, the NES has 10 times as much cycles in one frame than the Atari has during V-blank.

Author:  DementedPurple [ Wed Jan 24, 2018 9:41 am ]
Post subject:  Re: CRT in extreme slow motion

psycopathicteen wrote:
Wow, the NES has 10 times as much cycles in one frame than the Atari has during V-blank.

But to be fair, most, if not all of the graphics rendering is done simultaneously with the TV scanning, so it’s able to do more game logic during V-blank

Author:  tokumaru [ Wed Jan 24, 2018 10:09 am ]
Post subject:  Re: CRT in extreme slow motion

psycopathicteen wrote:
Wow, the NES has 10 times as much cycles in one frame than the Atari has during V-blank.

It's more like... 5 times, no?

Author:  lidnariq [ Wed Jan 24, 2018 10:35 am ]
Post subject:  Re: CRT in extreme slow motion

Most 2600 kernels seem to render 256x192, so that should be 228÷3×(262-192) = 5320 cy

I assume the 10x was assuming a full 224 scanlines rendered on the 2600 (leaving 2888cy during vblanking), but few games did that because it's just so little time.

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