Writing Device Drivers

uwritec(9F) and ureadc(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 9-4 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,
	   	ddi_put8(xsp->data_access_handle, &xsp->regp->csr,
	   	 * this device requires a ten microsecond delay
	   	 * between writes
	   pm_idle_component(xsp->dip, 0);
 	return (0);