VGA controller

Discussion in 'VHDL' started by hong.kei.chan.90, Jan 9, 2013.

  1. Hi,

    I was wondering if anyone has any experience programming a VGA controller using the DE1 or DE2 board to draw lines or shapes. This is a project that my professor proposed and I was wondering how hard this actually is.

    hong.kei.chan.90, Jan 9, 2013
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  2. hong.kei.chan.90

    o pere o Guest

    Your board documentation will probably give you some hints on how to get
    started. Essentially, you have to generate 5 signals hsync, vsync an RGB

    For the basic 640 x 480 mode you may be ok with a 25 MHz clock. An
    horizontal counter counting 0 to 799 and a vertical counter counting 0
    to 525 give the basic coordinates.

    You output hsync when hcounter is between 0 an 95, and output vsync when
    vcounter is between 0 and 1. You provide your information on the R, G
    and B lines when the horizontal counter is between 96+16 and 96+16+640
    and the vertical counter between 2+10 and 2+10+480. Have a look at basic
    timing diagrams available on the web.

    o pere o, Jan 9, 2013
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  3. hong.kei.chan.90

    KAY Guest

    Thanks for the reply Pere. One more question: Is there be a difference between a VGA controller and a VGA controller with hardware acceleration? If there is what is the difference?
    KAY, Jan 11, 2013
  4. hong.kei.chan.90

    o pere o Guest

    There may be some semantics issues here, but let's say there is a huge
    difference. A VGA controller simply maps bits (pixels) stored in some
    kind of memory onto the 5 signals of the VGA interface. Hardware
    acceleration means computing those bits (pixels) efficiently from a set
    of primitives (lines, polygons...).

    o pere o, Jan 11, 2013
  5. hong.kei.chan.90

    GaborSzakacs Guest

    Pere has talked about generating the video scan, but usually a harder
    issue is managing a frame buffer. For simple line drawing it is also
    possible to work without a frame buffer by using logic to determine
    whether a given pixel falls on a line. Very early video games like
    Pong had no frame buffer. For general drawing, however the frame
    buffer actually makes life easier as it allows unlimited numbers of
    drawing objects.

    Video display requires reading the frame buffer in advance of the
    output raster, incorporating a FIFO to avoid requiring the external
    RAM buffer to be read synchronously to the frame.

    Typically the frame buffer is structured as having a separate read/write
    port for "processor" or "graphics enginge" access for drawing. Strictly
    speaking a graphics engine does not need to read the frame buffer for
    creating new objects, but most graphics engines incorporate the ability
    to copy regions of the screen to another area (Google for "bitblt").

    All in all the difficulty of this project probably hinges on the ease
    of use of any available external memory controller.

    -- Gabor
    GaborSzakacs, Jan 11, 2013
  6. hong.kei.chan.90

    KAY Guest

    Thanks Gabor and Pere for your inputs! I think I have a better idea of the work necessary for the line drawing project.

    How does this sound?
    -using the 514K SRAM for the frame buffer.
    -having a graphics controller(with Direct memory access) that will take a start and end pixel location, and a command from the CPU> With a write command say '01' this will store the data into memory

    Right now, to my understanding without this "graphics controller" the CPU would be writing directly to the memory(which is rather slow) and by implementing this graphics controller the speed of the process will be increased significantly.

    Does this make sense?

    Thanks in advance.
    KAY, Jan 16, 2013
  7. hong.kei.chan.90

    Stef Guest

    In comp.lang.vhdl,
    Yes, a line drawing primitive is a good start. For inspiration, you
    could read some datasheets and user manuals for old graphics
    controllers like the HD63484 and AM95C60. Maybe you can have a look
    at newer controllers, but I suspect they are far too complex and
    documentation may not be fully available.

    Stef (remove caps, dashes and .invalid from e-mail address to reply by mail)

    All theoretical chemistry is really physics; and all theoretical chemists
    know it.
    -- Richard P. Feynman
    Stef, Jan 16, 2013
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