17.2.1 Interrupt Attribute

The interrupt attribute tells the compiler that the function is an interrupt handler. Use of this attribute is optional when building interrupt handlers for Cortex-M devices, but it is recommended to ensure that the compiler generates code to align the stack pointer on an 8 byte boundary upon function entry. This attribute is mandatory when writing interrupt handlers for Cortex-A devices, as the compiler must generate context switch code for interrupt handlers on such devices. For example:

void __attribute__((interrupt)) hoppy (void)
{
  // interrupt code goes here
}

When programming in C++, the interrupt handler symbol must be allocated to the C namespace, which can be accomplished using extern "C" with the definition, for example:

extern "C"
void __attribute__((interrupt)) hoppy (void)
{
  // interrupt code goes here
}