Calculate Threshold Counts

The settings for the threshold N_{CLKMON_THRESH} registers depends on the following parameters:

• Frequency of the base clock, F_{BASE_CLK}
• Number of base clocks programmed for the base time period, N_{BASE_CLK_CYCLES}
• Frequency threshold of the monitored clock, F_{MON_CLK}

A threshold setting can be calculated using the following equation:

Example

In this example, the following is assumed:

• REF_CLK is used with a 33 MHz clock frequency
• CLKMON0_BASE [CLK_CYCLES] is set = 10000
• Desired lower threshold frequency for the APU clock is 1000 MHz

Because the APU clock is divided by 4 before being presented to the ClkMon channel (see table in Monitored Clocks), the F_{MON_CLK} is actually 250 MHz.

From the equation, the clock threshold is 127EDh (75,757d). Bound the accuracy using ClkMon 0 by programming the CLKMON0_THRESH_L and CRP.CLKMON0_THRESH_H registers.

The result is a sampling time of approximately 303 μs.