WatchDog Interrupt CPUSleep

[integrator]

Never mind. That may have helped, but did not fix the problem.

[dkinzer]

I emailed you my code.

I observed the issue that you described. I found that disabling the Timer0 and Timer2 interrupts before entering sleep mode, and then re-enabling them afterward, seemed to solve the problem.

I tried this on a hunch because of this statement in the datasheet section on sleep modes:

If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up.

In your app, the only interrupts enabled are the watchdog interrupt, Timer0 and Timer2 compare match A interrupt, and the three USART0 interrupts. It didn't seem necessary to disable/re-enable the USART interrupts in my test but in the actual application it might be necessary to disable at least the "data received" interrupt.