When an interrupt occurs, the interrupt service routine (ISR) is executed. The kernel initially treats the ISR code as part of the context of the interrupted task until the osEnterISR function is invoked. This call explicitly marks the beginning of the interrupt handler context. If any system operations performed within this section require the scheduler, their execution will be deferred until the corresponding osLeaveISR function is called. In the case of nested interrupts, the deferred scheduler will be executed only when the final, outermost osLeaveISR call is performed.