error: undefined reference to `_CLI'
It is important to notice that accessing 16-bit registers are atomic operations. If an interruptoccurs between the two instructions accessing the 16-bit register, and the interrupt codeupdates the temporary register by accessing the same or any other of the 16-bit Timer Registers,then the result of the access outside the interrupt will be corrupted. Therefore, when boththe main code and the interrupt code update the temporary register, the main code must disablethe interrupts during the 16-bit access.
I also need to add sei(); to restore i-bit now right?