Writing Device Drivers

Interrupt Handler Functionality

The driver framework and the device each place demands on the interrupt handler. All interrupt handlers are required to do the following tasks:

The following example shows an interrupt routine for a device called mydev.

Example 8–9 Interrupt Example

static uint_t
mydev_intr(caddr_t arg1, caddr_t arg2)
    struct mydevstate *xsp = (struct mydevstate *)arg1;
    uint8_t     status; 
    volatile    uint8_t  temp;

     * Claim or reject the interrupt.This example assumes
     * that the device's CSR includes this information.

    /* use data access routines to read status */
    status = ddi_get8(xsp->data_access_handle, &xsp->regp->csr);
    if (!(status & INTERRUPTING)) {
        return (DDI_INTR_UNCLAIMED); /* dev not interrupting */
     * Inform the device that it is being serviced, and re-enable
     * interrupts. The example assumes that writing to the
     * CSR accomplishes this. The driver must ensure that this data
     * access operation makes it to the device before the interrupt
     * service routine returns. For example, using the data access
     * functions to read the CSR, if it does not result in unwanted
     * effects, can ensure this.
    ddi_put8(xsp->data_access_handle, &xsp->regp->csr,

    /* flush store buffers */
    temp = ddi_get8(xsp->data_access_handle, &xsp->regp->csr);
    return (DDI_INTR_CLAIMED);

Most of the steps performed by the interrupt routine depend on the specifics of the device itself. Consult the hardware manual for the device to determine the cause of the interrupt, detect error conditions, and access the device data registers.