NSTimer and seg faults

FROM : Gregory Short
DATE : Wed Mar 12 21:56:15 2008

Howdy all, first-time poster here. I'm pretty new to Objective-C and 
it's associated run-time environment, so I apologize if this is a 
total newbie question that has been answered before (I couldn't find 
anything, but I might not know where to look.)
   My problem is this: I have an NSTimer which I set up in my NSView's -
awakeFromNib method. Also in -awakeFromNib, I set create an NSDate 
object as part of the NSView. This all works fine. The problem is, 
when my timer fires, if I try to do anything at all with the NSDate 
object I created before, the program chokes. Here's the relevant 
portion of the code (I've stripped out what appears to be irrelevant; 
if anyone wants to see more, that's fine.)

BlobView.h:

@interface BlobView : NSOpenGLView
{
   NSTimer* updateTimer;
   NSDate* lastUpdate;
}

- (void) updateTimer: (NSTimer *) timer;

@end



BlobView.m:

@implementation BlobView

- (void) awakeFromNib {
   lastUpdate = [NSDate date];
   NSLog(@"%lf", [lastUpdate timeIntervalSinceNow]); // This works fine

   updateTimer = [NSTimer scheduledTimerWithTimeInterval: 1.0 / 30.0
       target: self
       selector: @selector(updateTimer:)
       userInfo: nil
       repeats: YES];
}

- (void) updateTimer: (NSTimer *) timer {
   NSLog(@"%lf", [lastUpdate timeIntervalSinceNow]); // This produces a 
SIGBUS
}

@end