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Registered: ‎09-15-2008

Timer values in the XPS Timer core

I'm working on a design with the XPS Timer core which requires clock-cycle accuracy of the timer's generator output, and I'm having a little bit of trouble figuring something out from the datasheet for the core.


In generator mode, exactly how long is the interval between interrupts? The datasheet says that the timer value loaded into the "Load Register" is called the "generate value". That seems normal enough. But then on page 3 of the datasheet, there is this little gem:


"If the counter is set up as a down counter, the generate value is the number of clocks in the timing interval. The period of the GenerateOut signal is the generate value times the clock period. When the counter is set to count down, TIMING_INTERVAL = (TLRx + 2) x PLB_CLOCK_PERIOD".


It seems to say two different things - in one, the number of clocks in each interval is whatever value I load into TLR. In the other, the number of clocks per interval is (TLR + 2) . Which one is it?

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