Using DMtimer pins to measure pulse width

I’m trying to use the timer pins (gpio2[2…5]) to measure pulse with on a BBB with the 25 MHz clock. The pin mud mode is correctly set to 2 and pull up/down are disabled and capture mode is set on the timers. When I connect a push button attached to 3.3v to one of the four timer pins I correctly get capture interreupts on low to high and high to low transitions and I can measure the timer difference between them without issue.

However, if I set up a signal generator for 50 Hz 3.3v square wave and attach it to a timer pin, I get no interrupts at all. Looking on a 'scope at the timer pin, the pulse train amplitude has drop from 3.3 volts to about 1.3v. Does anyone have any ideas on what would cause such a drop in amplitude?

Thanks for any suggestions.

Bob Stewart

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