ausmbus_read_byte
error = ausmbus_read_byte(sc, vp, I2C_F_STOP);
error = ausmbus_read_byte(sc, vp, I2C_F_STOP);
error = ausmbus_read_byte(sc, &low, 0);
error = ausmbus_read_byte(sc, &high, I2C_F_STOP);
static int ausmbus_read_byte(void *arg, uint8_t *vp, int flags);