On Tue, 12 Feb 2002, Andy Isaacson wrote:
> On Tue, Feb 12, 2002 at 10:17:55AM -0700, Kevin Geiss wrote:
> > It's an LCD microdisplay, about 2 inches tall and 3 inches wide. it has
> > a resolution of 800x600 and 8-bit color. it's meant to be held up to your
> > eye for viewing. the optics are quite nice, you don't have to squint or
> > anything to see it. It's called the 'Optiscape II' and it was made by
> > Inviso who is now owned by Three Five Systems.
> [snip]
> > The microdisplay is a bit wierd in its mode of operation. When you want to
> > write a pixel value to it, you have to write 32 pixels at a time, on a
> > 32-pixel boundary! (8 32-bit words at a time, on an 8 32-bit word boundary).
> > Also, the memory you write the pixels into is a bit slow; if you write at
> > full speed it kinda causes problems. in my frame buffer i delay for one
> > microsecond between each write on a 450 MHz AMD K6-2 system.
> [snip]
> > So, what i need to do is figure out how to intercept accesses to the
> > frame buffer memory to enforce the memory write speed limit and the
> > 32-pixel-at-a-time rule.
>
> Implement a driver using the ShadowFB layer; your RefreshArea routine
> will just have to do the write slow enough to keep the hardware happy.
>
> (Hmm, I wonder if there's any way to "schedule" those writes so that the
> X server doesn't have to sit there waiting for the memory to catch up
> after every screen modification... well, 32 bytes per microsecond is 30
> MB / second, so it shouldn't be so slow as to be unusable -- just about
> 3 times slower than a standard PCI framebuffer.)
The wait is too short to do much other than busy wait. Rescheduling
with usleep(1) will likely give you a minimum delay of 10 MILLISECONDS.
Mark.
>
> Look at the various drivers in xc/programs/Xserver/hw/xfree86/drivers/*
> to see how ShadowFB is used. The MGA is sorta the original standard...
>
> -andy
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