Re: [Linux-fbdev-devel] vga256fb

[Geert U. <ge...@li...>]

On Mon, 14 May 2001, James Simmons wrote:
> > The other problem is that without a PACKED_PIXEL display all the
> > userspace currently available will not work.
> 
> Their is not much you can do to get around this besides writing a native
> framebuffer :-). A emulation mode is way to slow. In theory you could this
> for atari and ilbm modes but it would go so sloooow.

I've been thinking about this. I see 2 possible approaches for emulation:

  - Map the fake frame buffer read-only. Trap all write accesses and convert
    between packed pixels and native format in the trap handler. Expensive due
    to many context switches.

  - Map the fake frame buffer read-only. In the trap handler, make the page
    writable and rerun the write. In a timer handler, convert all pages that
    are writable and make them read-only again. Faster, but more visible delay
    (however, if the timer handler runs sufficiently frequent you won't
    notice).

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@li...

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds