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VGA.spin Explained! (bug found?) — Parallax Forums

VGA.spin Explained! (bug found?)

RaymanRayman Posts: 14,876
edited 2011-08-19 17:02 in Propeller 1
VGA.spin is a very complex driver and very hard to understand.
But, it's the basis for a lot of my LCD drivers, so I've had to decipher it...
I think I've got it mostly figured out.

Anyway, I've added my notes to the original VGA.spin file to other people
figure out what's going on.
Regarding the possible bug, I think on my line 440:
sub x,
should be
sub t1,
But, it would only show up when asking for a very slow pixel clock...

VGA_Explained.spin
spin
spin
VGA_Explained.spin
107K

Comments

  • RaymanRayman Posts: 14,876
    edited 2011-08-18 15:47
    PS: I'm not 100% on the blank and sync timing for interlaced mode.
    Did some web searching for what the exact syncs should look like for interlaced VGA, but couldn't find anything...
    In interlaced mode, the vsync is different for even and odd fields.
    I think I see what's going on, but it'd be nice to find a reference so I could be sure that I'm reading it right
    (and also that it's being done right :)
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-08-18 19:32
    Rayman,

    This is enormously helpful! Thanks for making the effort to do this and to share it with the rest of us!

    -Phil
  • TubularTubular Posts: 4,717
    edited 2011-08-18 20:03
    Absolutely brilliant effort Rayman. I think you just saved me a heap of time, which of course I'll have to spend on more prop projects.

    Perhaps this could be the beginning of an "UnSpun" series - taking a real close, easy to follow look at some of the more mysterious prop code.
  • Martin HodgeMartin Hodge Posts: 1,246
    edited 2011-08-18 21:34
    More of this kind of thing needs to be done! There can never be too much explanation.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2011-08-19 00:58
    @ first glance........ Nice

    ff
  • ColeyColey Posts: 1,110
    edited 2011-08-19 01:05
    Rayman, I agree, this is really helpful, thank you!
    I really like the way you have expanded the explanation over several lines not just a few short comments.

    Regards,

    Coley
  • nohabnohab Posts: 96
    edited 2011-08-19 02:34
    Excellent !!!
    Both to get the VGA-driver explained but also a quite complex assembler program with so much explanation is just GREAT, thanks a lot!
  • potatoheadpotatohead Posts: 10,261
    edited 2011-08-19 09:33
    I am eager to read this. Great job! Much appreciated.
  • jazzedjazzed Posts: 11,803
    edited 2011-08-19 09:44
    Tubular wrote: »
    Perhaps this could be the beginning of an "UnSpun" series ...
    Great name!

    Good work Rayman.
  • RaymanRayman Posts: 14,876
    edited 2011-08-19 17:02
    Thanks for all the nice comments everybody.
    Please let me know if anybody finds errors or ommissions and I'll try to make it better.

    I like "UnSpun" too... Maybe I should change the title of this thread to: VGA.spin ---> UnSpun !
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