# Intro to Embedded Systems Lecture Notes: February 7th, 2023

## Using Interrupts
```c
#define INTERRUPT_PINS 0x03

int main(void)
{
    P4IE |= INTERRUPT_PINS;                                     // Local interrupt enable
    P4IFG |= INTERRUPT_PINS;
    P4IES |= INTERRUPT_PINS;

    _enable_interrupts();                                       // Global interrupt enable
    __bis_SR_register(GIE);

    while (true)
    {
        ...
    }
     return 0;
}

// Port 4 interrupt service routine
void __attribute__ ((interrupt(PORT4_VECTOR))) Port_4 (void)
{
    ...
}
```

## Interrupt Servicing Summary
1. Interrupt Pending
2. Complete Current Instruction
3. Clear SR
4. Retrieve starting address of ISR & put address in PC
5. Execute ISR
6. Pop SR and PC from stack
7. Continue to main program

## Multiple Interrupts
### Three Types:
1. Reset Interrupt
2. Maskable Interrupt
    - ADC, port, timer, e_USCI
    - User-asserted event
3. Non-Maskable Interrupt
    - Fault, error detection
    - Oscillator fault
    - Flash key violation

## Priority of Interrupts
1. Timers
2. e_USCI
3. ADC
4. Port