graphics on G4

[Justin Hibbits]

On Fri, Mar 06, 2009 at 07:06:26AM -0500, Justin Hibbits wrote:
> > >> Did you ever discover whether writing to random bits of the framebuffer 
> > >> without ever having run X also causes this problem?
> > >> -Nathan
> > > 
> > > Yes, I did perform that test, and it does cause the problem as well.  For me it
> > > hangs when starting a new process some time later, so can be tested somewhat
> > > easily by performing a buildworld after doing the graphics test.
> > 
> > My card, at least, has a framebuffer BAR that is 128 MB long, but only 
> > actually has 32 MB of graphics RAM. Writing anything to that 32 MB does 
> > not cause problems, but of course writing beyond that kills the machine, 
> > since that memory region does not actually exist. Is this true for yours 
> >   as well?
> > -Nathan
> 
> My card has 256MB of graphics RAM, and according to dmesg allocates that size
> block, plus 64k in the 256MB region before it.  I haven't yet tested what
> address byte actually causes the crash, but that can be determined relatively
> easily.  What I'm guessing, though, is writing to anything past (end - 32k) will
> cause the crash.  I'll see if I can test this weekend.
> 
> So, short answer to your question: it's not quite true for me, because it
> happens when I write to what should be inside graphics RAM.
> 
> - Justin

Nathan-

Attached is a simple program I wrote that just writes a straight line down the
first column of the framebuffer.  It reliably kills my system while running a
'make buildworld' within a few minutes of running this program.

(Possibly) Relevant Details:

ATI Radeon 9600PRO, 256MB edition.
1280x1024x8 framebuffer
1.25GiB RAM

- Justin