ginge/OpenServo — pull request #2 by Corna (2014-11-10 07:51:23+00:00)
Title: Removed cli() and sei() inside ISR(USART_RXC_vect)

As reported here http://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html, at "Nested interrupts", the AVR hardware automatically clears the global interrupt flag at the start of the ISR