ulpt_write_callback Function

The ulpt_write_callback function transfers data from user space to the printer (to be printed). Recall that this function is the callback for a bulk OUT endpoint, so it’s executed before and after a bulk OUT transfers data.

The following is the function definition for ulpt_write_callback:

static void
ulpt_write_callback(struct usb_xfer *transfer, usb_error_t error)
{
        struct ulpt_softc *sc = usbd_xfer_softc(transfer);
        struct usb_fifo *fifo = sc->sc_fifo_open[USB_FIFO_TX];
        struct usb_page_cache *pc;
        int actual, max;

        usbd_xfer_status(transfer, &actual, NULL, NULL, NULL);

        if (fifo == NULL)
                return;

        switch (USB_GET_STATE(transfer)) {
      case USB_ST_SETUP:
      case USB_ST_TRANSFERRED:
setup:
                pc = usbd_xfer_get_frame(transfer, 0);
                max = usbd_xfer_max_len(transfer);
                if (usb_fifo_get_data(fifo, pc, 0,
 max,
                    &actual, 0)) {
                      usbd_xfer_set_frame_len(transfer, 0, actual);
                      usbd_transfer_submit(transfer);
                }
                break;
        default:
                if (error != USB_ERR_CANCELLED) {
                        /* Issue a clear-stall request. */
                        usbd_xfer_set_stall(transfer);
                        goto setup;
                }
                break;
        }
}