[avr-chat] Timer1 Frequency Doubling in ATMEGA128 App

[Kevin Neff]

I am in the midst of designing a real time embedded system that uses
the ATMEGA128.  Time keeping is handled by Timer1, a 16-bit timer.
Every second, an LED on the board is toggled or or off to make it easy
to see if the system crashes.

Depending on which power supply I use, I get the light blinking at 1 or
2 Hz.  The STK500 supply produces a reliable 1 Hz, but a 12 VDC supply
through a 7805 5VDC linear regulator produces 2 Hz.  It's also interesting
to know that if I reset (pull RESET\ low) the uC, it goes back to 1 Hz.

Does anyone have a guess as to what's happening here?

--Kevin Neff