SSD13XX_CONTRAST
ret = ssd130x_write_cmd(ssd130x, 1, SSD13XX_CONTRAST);
ret = ssd130x_write_cmd(ssd130x, 2, SSD13XX_CONTRAST, ssd130x->contrast);
ret = ssd130x_write_cmd(ssd130x, 2, SSD13XX_CONTRAST, 0x80);