6.4.3 Status Register
The Status Register (CPU.SREG) contains information about the result of the most recently executed arithmetic or logic instructions. This information can be used for altering the program flow to perform conditional operations.
CPU.SREG is updated after all ALU operations, as specified in the Instruction Set Summary section, which will, in many cases, remove the need for using the dedicated compare instructions, resulting in a faster and more compact code. CPU.SREG is not automatically stored or restored when entering or returning from an Interrupt Service Routine (ISR). Therefore, maintaining the Status Register between context switches must be handled by user-defined software. CPU.SREG is accessible in the I/O memory space.