uwritec(9F) and uread(9F)

Another example of programmed I/O might be a driver writing data one byte at a time directly to the device's memory. Each byte is retrieved from the uio(9S) structure using uwritec(9F), then sent to the device. read(9E) can use ureadc(9F) to transfer a byte from the device to the area described by the uio(9S) structure.

Example 10-4 Programmed I/O write(9E) Routine Using uwritec(9F)

static int
xxwrite(dev_t dev, struct uio *uiop, cred_t *credp)
{
        int    value;
        struct xxstate     *xsp;

        xsp = ddi_get_soft_state(statep, getminor(dev));
        if (xsp == NULL)
                return (ENXIO);
        if the device implements a power manageable component, do this:
        pm_busy_component(xsp->dip, 0);
        if (xsp->pm_suspended)
                ddi_dev_is_needed(xsp->dip, normal power);

        while (uiop->uio_resid > 0) {
                /*
                 * do the programmed I/O access
                 */
                value = uwritec(uiop);
                if (value == -1)
                       return (EFAULT);
                ddi_put8(xsp->data_access_handle, &xsp->regp->data,
                    (uint8_t)value);
                ddi_put8(xsp->data_access_handle, &xsp->regp->csr,
                    START_TRANSFER);
                /*
                 * this device requires a ten microsecond delay
                 * between writes
                 */
                drv_usecwait(10);
        }
        pm_idle_component(xsp->dip, 0);
        return (0);
}