nc_register_read
retval = nc_register_read(dev, reg, vp);
if ((retval = nc_register_read(dev, REG_STATUS, &vp)) < 0) {
if ((retval = nc_register_read(dev, REG_USBCTL, &vp)) < 0) {
if ((retval = nc_register_read(dev, REG_TTL, &vp)) < 0) {
retval = nc_register_read(dev, REG_STATUS, &vp);