Is there a way of telling if sei()/interrupts() or cli()/noInterrupts() was last called?

I need this to be able to enable interrupts, execute some code and set interrupts disable interrupts if they where disabled.

Here is some sample code:

void function_requiring_interrupts(void) {
    bool interruptsEnabled = getInterrupsState(); // what function / variable here?


    // Code requiring interrups are enabled

    if(!interruptsEnabled) {

1 Answer 1


One way of doing this is to save, and then later restore the SREG status register, thus saving and later restoring the interrupt status to whatever it was, thus:

  uint8_t oldSREG = SREG; // Save the status

  // Do stuff, as little as possible.

  SREG = oldSREG;

Also, the rationale described in the question has inherent problems: If some other code already had interrupts disabled, and your code enables interrupts, data corruption or program failure could occur. Any "interrupt-disabled" block of code would be expecting all registers and memory / variables to remain untainted, while enabling interrupts can cause that to change.

Therefore the reverse logic, as in the code fragment above, is best practice: Explicitly disable interrupts for your own code as needed, but restore interrupts as soon as possible, then proceed with the rest of your processing.

  • \$\begingroup\$ Anindo is right about the warning. You should never enable interrupts in a library or other call that is not specifically designed to do that. Code that has interrupts disabled did so for a reason and enabling interrupts in your library routine could cause all sorts of havoc with the other code. \$\endgroup\$
    – james
    Apr 19, 2013 at 16:46
  • \$\begingroup\$ Would it matter if an interrupt were to occur after saving the status register, but before disabling interrupts? \$\endgroup\$
    – Shepmaster
    May 14, 2016 at 23:28

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