Re: Question about the video device driver

On Mon, 10 Jan 2000, Shuangjun Zhu wrote:

quoted

I'm a newbie in the X domain,
where can I get the information about showfb?
As I know, there is no hardware for MPC823 FADS that can do the
conversion from RGB data stored in system memory,
we must do it using software.

So, where I should start?
Any suggestion?

  Shadowfb is a "layer" (using the X terminology) which 
is initialized after framebuffer rendering is setup.  It
is given a callback function when initialized.

typedef void (*RefreshAreaFuncPtr)(ScrnInfoPtr, int, BoxPtr);

Bool
ShadowFBInit (
   ScreenPtr           pScreen,
   RefreshAreaFuncPtr  refreshArea
);

 The shadowfb encapsulates all rendering into that buffer
and gives the driver a callback telling it which rectangles
of the buffer have been updated.

  What can be done is that one can setup a framebuffer in 
system memory and get callbacks telling which parts need to
be copied into the real hardware framebuffer, hence the
name - you have a buffer and its shadow.   It is safe to
copy areas larger than the rectangles you are told to update.
That way you can reduce your refreshArea function to copying
and translating only macroblocks.

  There are examples in some other drivers such as the
glide driver which uses it on a write-only framebuffer or
the MGA driver which uses it for effects like rotating
the screen.

  What format is the hardware buffer in?  What macroblock
size?

For the MPC823 FADS board, video controller is in the CPM, part of 
the CPU, and video encoder is ADV7176, video memory is map to 
the system memory.  It can support NTSC/PAL display.

MPC823 can support RGB and YCr Cb, but for Analog Devices ADV7176
video encoder,  it can only support 4:2:2 YCr Cb(CCIR 601) format.

I do not know what the macroblock's meaning is.

Mark.

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