Vertical seam in 1942

Discuss emulation of the Nintendo Entertainment System and Famicom.

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nflga
Posts: 7
Joined: Mon Feb 18, 2019 3:08 pm

Vertical seam in 1942

Post by nflga » Mon Feb 18, 2019 3:32 pm

Hey guys,

First of all, thank you for all the time you've invested in both the wiki and in these forums.
I'm grateful for the tons of great info and all the help you have given me (indirectly, from reading other topics, but still).

I'm seeing a seam at the top of the screen while testing 1942.
Now, from what I gather, it's probably a bug, but my code *seems* to be correct.
Tried to load up messen but my mono version is too old.
However I loaded up https://github.com/fogleman/nes and he has the same problem.
Now I'm not sure if this is expected behaviour, or if I truly have a problem, the timing logic can be a bit tricky, and I might just be a row behind. My implementation is based on the (skinny) scrolling and timing docs.

As such, the question is simple, is the seam supposed to be visible?
This only happens in vertical scroll. Horizontal is working fine.

I've attached the output that I'm getting and a dump of the nametable data at that point.

Thanks in advance!
Attachments
nametables
nametables
output
output

tepples
Posts: 21755
Joined: Sun Sep 19, 2004 11:12 pm
Location: NE Indiana, USA (NTSC)
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Re: Vertical seam in 1942

Post by tepples » Mon Feb 18, 2019 3:57 pm

Japanese and North American TVs of the time tended to cut 8 to 16 pixels off the top and bottom. Incidentally, this is also the source of "256x224" semi-misconception. See "Overscan" on the wiki.

nflga
Posts: 7
Joined: Mon Feb 18, 2019 3:08 pm

Re: Vertical seam in 1942

Post by nflga » Mon Feb 18, 2019 4:17 pm

Hi tepples,

Thanks for the help.
I thought it could be overscan related, but I'm not that confident about the code just yet :)

Thank you very much!

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