Shop OBEX P1 Docs P2 Docs Learn Events
VSCL / VCFG Buffered? — Parallax Forums

VSCL / VCFG Buffered?

asterickasterick Posts: 158
edited 2007-01-24 14:47 in Propeller 1
Studying the VGA Bitmap 512x384 bitmap source, I've noticed it changes the VSCL register before it does a WAITVID for the blanking periods / porch signals. I was just wondering if changing the VSCL register while the serializer is running, if it's buffered until the frame has been exited to maintain consistant timing?

Comments

  • Ym2413aYm2413a Posts: 630
    edited 2007-01-23 20:13
    Wow, that a really good question.
    I never thought about that....
    Asterick? since your mind is on the topic what would be the easiest way of testing to see if there is a buffer?

    Funny enough I've been thinking of changing the VSCL during a raster to play around with color generating in this idea I got.
    If I get lucky and find anything interesting I will inform you right away buddy. ^^

    --Andrew Arsenault
  • asterickasterick Posts: 158
    edited 2007-01-23 20:44
    The EASY way would be to do something like:

    mov VSCL, fastVscl
WAITVID $FF00FF00, pixels
mov VSCL, slowVscl
nop
nop
nop
nop
nop
mov VSCL, fastVscl
WAITVID $FF00FF00, pixels



    and hook the chip up to a logic probe, and see if it outputs a perfect square wave.

    Another method would be to wire the video generator up to the audio output and change the rate for the last 31 of 32 samples, have one tone be like 9khz and another be like 4.5khz, since it's easy to identify the difference between.
  • Ym2413aYm2413a Posts: 630
    edited 2007-01-23 20:54
    Okay, I'm leaving work early today so I can test this out before I take my lovely women out tonight!
    I had a feeling you were already thinking of ways to test this before you even wrote the post. That's why I asked.
  • asterickasterick Posts: 158
    edited 2007-01-23 21:14
    Haha, [noparse]:)[/noparse] Well, that's the 'easy' way or so. We have a logic probe here at work, so it would be simple for me to do. Alas, I have no propeller.

    Flying blind is awesome.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-01-23 22:41
    Ok got some info from the source, VSCL is buffered, VCFG is not.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • asterickasterick Posts: 158
    edited 2007-01-23 22:43
    Awesome. That's exactly what I expected it to be. [noparse]:)[/noparse] Thanks a million, that is EXTREMELY helpful.
  • Ym2413aYm2413a Posts: 630
    edited 2007-01-24 14:47
    Oh wow, I was just going to post what I found. (lol)
    Well, running the tests was fun anyway.
    I came up with the same thing Paul stated.
    smile.gif
Sign In or Register to comment.