Analog Devices adsp-2100 Manual page 146

6 Timer
One interrupt occurs every (TPERIOD +1) * (TSCALE +1) cycles. To set the
first interrupt at a different time interval from subsequent interrupts, load
TCOUNT with a different value from TPERIOD. The formula for the first
interrupt is (TCOUNT+1) * (TSCALE+1).
If you write a new value to TSCALE or TCOUNT, the change is effective
immediately. If you write a new value to TPERIOD, the change does not
take effect until after TCOUNT is reloaded.
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