SET_DISPLAY_CLEAR
st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 1600, err);
st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 1600, &err);
st7920_spi_write(st7920->spi, SET_DISPLAY_CLEAR, NULL, 1600, &err);