Re: Screen regen buffer at 0x00b8000

[Geert Uytterhoeven <geert@linux-m68k.org>]

On Fri, 20 May 2005, Richard B. Johnson wrote:
> On Fri, 20 May 2005, Jan-Benedict Glaw wrote:
> > On Fri, 2005-05-20 09:48:35 -0400, Richard B. Johnson
> > <linux-os@analogic.com> wrote:
> > >     len = getpagesize();
> > >     if((fd = open("/dev/mem", O_RDWR)) == FAIL)
> > >         ERRORS("open");
> > >     if((sp = mmap((void *)SCREEN, len, PROT, TYPE, fd,
> > > SCREEN))==MAP_FAILED)
> > >         ERRORS("mmap");
> > 
> > Maybe you'd better not fiddle with physical memory, but use the device
> > abstraction that's ment to offer that interface? That is, use a
> > framebuffer driver and open /dev/fb* .

/dev/vcs*?

> No room for any more drivers. This just writes to a small LCD on an
> embedded controller. There should be no reason why I can't
> write directly to the physical memory. Anything written to the
> physical screen buffer will show up on the screen, as long
> as page zero is selected.
> 
> I think that I've discovered a bug. I know that what I have written gets
> to the screen buffer because I can read in back! This doesn't make
> any sense.

Even if it's only in the CPU cache, of course you can read it back (using the
CPU, not DMA ;-).

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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
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