EIC Handler

typedef struct
{
    PORT_PINCFG_Type pin_cfg;
    PORT_PMUX_Type pin_mux;
    uint16_t driveRegister; /* == 0 or (1<<11) */
} port_cfg;


port_cfg port_config[16] = {
    [0].pin_cfg.bit = { .PMUXEN = 0, .INEN = 1 },
    /* [1...6] */
    [7].pin_cfg.bit = { .PMUXEN = 1, .INEN = 1 },
    [8].pin_cfg.bit = { .PMUXEN = 1, .INEN = 1 },
    [9].pin_cfg.bit = { .PMUXEN = 1, .INEN = 1 },
    /* [10...15] / [0...6] */
    [7].pin_mux.bit = { .PMUXO = MUX_PA11E_TC1_WO1 },
    [8].pin_mux.bit = { .PMUXO = MUX_PA11C_SERCOM0_PAD3 },
    [9].pin_mux.bit = { .PMUXO = MUX_PA11C_SERCOM0_PAD3 },
    /* [10...15] */
};

void EIC_Handler(void)
{
    // a shared interrupt handler for changes on five different external pins:

    // EXTINT0 = PA00 = SEL - interrupt on rising or falling edge
    // EXTINT1 = PA01 = PH0 - interrupt on rising or falling edge
    // EXTINT2 = PA02 = PH1 - interrupt on rising or falling edge
    // EXTINT3 = PA03 = PH2 - interrupt on rising or falling edge
    // EXTINT4 = PA04 = PH3 - interrupt on rising edge
    // PA11 = output

    uint32_t flags = EIC->INTFLAG.reg; // a 1 bit means a change was detected on that pin

    // clear EXTINT0-4 flags, if they were set.
    EIC->INTFLAG.reg = (flags & 0x1F); // writing a 1 bit clears the interrupt flags

    // mask the 4 lowest bits and use them as the address of the desired drive register
    uint32_t localSelectedDriveRegister = PORT->Group[GPIO_PORTA].IN.reg & 0xF;

    PORT->Group[GPIO_PORTA].OUTSET.reg = port_config[localSelectedDriveRegister].driveRegister;
    PORT->Group[GPIO_PORTA].OUTCLR.reg = (~port_config[localSelectedDriveRegister].driveRegister)&(1<<11);
    PORT->Group[GPIO_PORTA].PINCFG[11] = port_config[localSelectedDriveRegister].pin_cfg;
    PORT->Group[GPIO_PORTA].PMUX[11>>1] = port_config[localSelectedDriveRegister].pin_mux;

    selectedDriveRegister = localSelectedDriveRegister;

    /*...*/
}