On Mon, Apr 04, 2005 at 09:59:22AM +0100, [EMAIL PROTECTED] wrote: > Jonathan Lundell wrote: > >Well, not actually a time warp, though it feels like one. > > > >I'm doing some real-time bit-twiddling in a driver, using the TSC to > >measure out delays on the order of hundreds of nanoseconds. Because I > >want an upper limit on the delay, I disable interrupts around it. > > > >The logic is something like: > > > > local_irq_save > > out(set a bit) > > t0 = TSC > > wait while (t = (TSC - t0)) < delay_time > > out(clear the bit) > > local_irq_restore > > > > From time to time, when I exit the delay, t is *much* bigger than > >delay_time. If delay_time is, say, 300ns, t is usually no more than > >325ns. But every so often, t can be 2000, or 10000, or even much higher. > > > >The value of t seems to depend on the CPU involved, The worst case is > >with an Intel 915GV chipset, where t approaches 500 microseconds (!).
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