SGP40_GET_SERIAL_NUMBER
reg[0] = SGP40_GET_SERIAL_NUMBER >> 8;
reg[1] = SGP40_GET_SERIAL_NUMBER & 0x00ff;
error = sgp40_cmdr(sc, SGP40_GET_SERIAL_NUMBER, NULL, 0, buf, 9);
.cmd = SGP40_GET_SERIAL_NUMBER,