Device Access Functions

Drivers use the ddi_get8(9F) and ddi_put8(9F) family of routines in conjunction with the handle returned by ddi_regs_map_setup(9F) to transfer data to and from a device. The DDI framework automatically handles any byte-swapping that is required to meet the endian format for the host or device, and enforces any store-ordering constraints the device might have.

The DDI provides interfaces for transferring data in 8-bit, 16-bit, 32-bit, and 64-bit quantities, as well as interfaces for transferring multiple values repeatedly. See the man pages for the ddi_get8(9F), ddi_put8(9F), ddi_rep_get8(9F) and ddi_rep_put8(9F) families of routines for a complete listing and description of these interfaces.

The following example builds on Example 7–1 where the driver mapped the device's CSR and data registers. Here, the driver's write(9E) entry point, when called, writes a buffer of data to the device one byte at a time.

static  int
pio_write(dev_t dev, struct uio *uiop, cred_t *credp)
{
    int  retval;
    int  error = OK;
    Pio *pio_p = ddi_get_soft_state(pio_softstate, getminor(dev));

    if (pio_p == NULL)
        return (ENXIO);
    mutex_enter(&pio_p->mutex);
    /*
     * enable interrupts from the device by setting the Interrupt
     * Enable bit in the devices CSR register
     */
    ddi_put8(pio_p->csr_handle, pio_p->csr,
      (ddi_get8(pio_p->csr_handle, pio_p->csr) | PIO_INTR_ENABLE));

    while (uiop->uio_resid > 0) {
    /*
     * This device issues an IDLE interrupt when it is ready
     * to accept a character; the interrupt can be cleared
     * by setting PIO_INTR_CLEAR.  The interrupt is reasserted
     * after the next character is written or the next time
     * PIO_INTR_ENABLE is toggled on.
     *
     * wait for interrupt (see pio_intr)
     */
        cv_wait(&pio_p->cv, &pio_p->mutex);

    /*
     * get a character from the user's write request
     * fail the write request if any errors are encountered
     */
        if ((retval = uwritec(uiop)) == -1) {
            error = retval;
            break;
        }

    /*
     * pass the character to the device by writing it to
     * the device's data register
     */
        ddi_put8(pio_p->data_handle, pio_p->data, (uchar_t)retval);
    }

    /*
     * disable interrupts by clearing the Interrupt Enable bit
     * in the CSR
     */
    ddi_put8(pio_p->csr_handle, pio_p->csr,
      (ddi_get8(pio_p->csr_handle, pio_p->csr) & ~PIO_INTR_ENABLE));

    mutex_exit(&pio_p->mutex);
    return (error);
}