4850 - Found the problem

Discussion in 'iMac' started by bizack, Apr 27, 2009.

  1. bizack macrumors 6502a

    Apr 21, 2009
    I can reproduce the ATI 4850 freeze by using the iTunes visualizer in fullscreen mode. So I wanted to see if this could help find the problem, and it did.
    I used the OpenGL Profiler that's included with the dev tools. I attached the profiler to the iTunes process, and dumped all the OpenGL calls. iTunes eventually crashed the profiler, leaving my computer in a state of limbo (not completely frozen... could still use expose to see what was on my desktop, but otherwise the computer was completely locked up.... but the profiler 'trapped' the iTunes process, which stopped it from completely freezing my machine). Sent a bug report to Apple. The problem is the OpenGL implementation in the ATI driver. I've tried to freeze my computer under Win XP in Boot Camp by playing Portal with the highest settings. No freezes, but all the Valve games use DirectX, not OpenGL. And yes, the version of OS X that ships with the iMac is a custom build. I now have a few applications that won't launch properly on my iMac, but work on my MacBook Pro with the exact same (major) build of OS X. The only difference is the hardware. There might be some CoreAudio conflicts with these machines as well. I'm debating waiting for a firmware update, or just downgrading to the default NVIDIA iMac.

  2. VulnoX macrumors member

    Apr 23, 2009
    The problem seems to be with using WiFi under load more than it is graphics under load. Is your WiFi on? Are you doing WiFi related things at the same time?
  3. bizack thread starter macrumors 6502a

    Apr 21, 2009
    I think this is a side effect. Wi-Fi is on, but I can freeze my machine while using iTunes visualizer and browsing via Safari 4.x, or by using iTunes visualizer with absolutely nothing else open.
    Drivers are pesky, pesky things. I wouldn't be surprised if there's an OpenGL call that freezes the machine because of an overrun into the memory space of another hardware component. The Wi-Fi driver is loaded at boot whether you have Wi-Fi turned on or off. It would be interesting to see if the load sequence of the graphics driver and the Wi-Fi driver are in-order or close to one another in memory space.
  4. Consultant macrumors G5


    Jun 27, 2007
  5. Cave Man macrumors 604

    Cave Man

    Feb 12, 2007
    Neander Valley, Germany; just outside Duesseldorf
    I think we ought to drop OpenGL and go back to POKEs and PEEKs.
  6. nss.aries macrumors member

    Feb 16, 2009
    Bizack try some test with airport disabled, please.
    Enabled: freezes everywhere
    Disabled: no freeze in 10 hours playing HDmovies, itunes visualizer, youtube playlists, painter images.

    Dunno why...
  7. arty2shock macrumors newbie

    Apr 9, 2009
    well, if it's a OpenGL Driver thing this would be a possible reason why FinalCut Pro kills my iMac when i start playback (immediately after rendering is complete)

    (assuming FinalCut Pro uses OpenGL ;)
  8. jmpage2 macrumors 68040


    Sep 14, 2007
    This is good investigatory work, but doesn't explain why so many people have either eliminated freezes by switching to wired Ethernet, or, have never had freezes at all.

    If an OpenGL call was causing the trouble it would seem that we ALL would have the problem, but many of us don't.

    I have run my iTunes Visualizer full screen for hours and hours and not a single lock up to date.
  9. rikun macrumors newbie

    Apr 8, 2009
    If it is true that the iMacs with the Nvidia cards experience absolutely no freezing, I too am considering downgrading my replacement. Wonder if Apple will refund the difference.:D
  10. 24usedtorock macrumors regular

    Apr 26, 2009
    Kind of funny how Nvidia got absolutely :apple:'ed on by ATI fans yet it seems now those same people have egg on face.
  11. jmpage2 macrumors 68040


    Sep 14, 2007
    Sure, until the fix comes out, oh ya, and for those of us not having the issue and playing Crysis and other games at FPS the GT130 can only dream about, we think those comments about egg on face are pretty funny stuff.
  12. GamaFu macrumors regular

    Apr 12, 2007
    I am just getting so confused about just what's causing all the freezing. I'd like to believe it's driver like bizack suggests, but how do we explain it freezes while watching videos on Hulu or YouTube? I don't believe browsers like Firefox or Safari use OpenGL, do they? I do know Flash Player utilizes hardware acceleration though. It just happens so randomly that I can have it not crash for 3 days, but keep lockup 2 or 3 times in one day. Mine never freezes while listening to internet radio with Visualizer on though.
  13. mstam macrumors member

    Apr 20, 2009
    It's one of the following issues:

    1. Conflict between the video and WiFi card (IRQ, memory)
    2. Bad batch of WiFi cards
    3. Bad batch of video cards

    #1 Can most likely be fixed w/ a firmware update.
  14. bizack thread starter macrumors 6502a

    Apr 21, 2009
    Well, I debunked my own theory. Turned Wi-Fi off and no freezes. Also used kextstat within the Terminal to see where the drivers were laid out in memory... calculated the address+size of the ATI driver (which isn't listed as 4850 btw) and the Broadcom driver. There's about 1 MB between the two in memory, so that squashes the theory of them being next to one another.
    Called Apple, went to second tier support where the problem wasn't acknowledged as being widespread. A replacement is being shipped out. And yes, if you request to have your credit card billed, you can have the replacement shipped before your defective machine is picked up. You'll be refunded when the defective machine is in Apple's tracking system. I guess I'll keep doing this until the problem is fixed, or my credit card's limit is reached...

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