rmi_spi_xfer
ret = rmi_spi_xfer(rmi_spi, &cmd, &page, 1, NULL, 0);
ret = rmi_spi_xfer(rmi_spi, &cmd, buf, len, NULL, 0);
ret = rmi_spi_xfer(rmi_spi, &cmd, NULL, 0, buf, len);