On Mon, 15 Dec 2014 14:19:32 -0600, Chris said: > On Mon, 2014-12-15 at 13:43 -0500, Valdis.Kletnieks@xxxxxx wrote: > > I'm pretty sure that's a timer for the i915 driver that detects if the > > GPU has gone into an infinite loop due to (usually) buggy programming from > > the operating system.... > > Thank you Valdis as far as the OS we're talking about Ubuntu not the > bios correct? More specifically, the i915 is actually a fully programmable CPU in its own right, but it's a crazy morass of interrupts and circular buggers and race conditions. The operating system (Ubuntu or what have you) actually send the i915 a program of what to display, and the i915 goes off and does it. Of course, missing a single interrupt or an off-by-one error in a circular buffer will cause the i915 to go off the rails and usually get hung in a hard loop. (It doesn't help that the i915 has a ton of wonky restrictions of the form "you can do this during a vertical retrace period, but only during the first half of a horizontal retrace". And yes, I'm pretty sure it actually enforces vertical and horizontal retrace timings on LCDs. Silly, huh? ;)
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