add SDM120 electricity meter library (only transmit works)

lib/sensor_sdm120.h

@@ -0,0 +1,54 @@
+/* This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+/** library to query measurements from eastron SDM120-ModBus electricity meter (API)
+ *  @file sensor_sdm120.h
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @date 2016
+ *  @note peripherals used: USART @ref sensor_sdm120_usart , GPIO @ref sensor_sdm120_gpio
+ */
+#pragma once
+
+/** a measurement response has been received */
+extern volatile bool sensor_sdm120_measurement_received;
+
+/** measurements offered by electricity meter */
+enum sensor_sdm120_measurement_type_t {
+	SENSOR_SDM120_VOLTAGE = 0,
+	SENSOR_SDM120_CURRENT,
+	SENSOR_SDM120_POWER_ACTIVE,
+	SENSOR_SDM120_POWER_APPARENT,
+	SENSOR_SDM120_POWER_REACTIVE,
+	SENSOR_SDM120_POWER_FACTOR,
+	SENSOR_SDM120_FREQUENCY,
+	SENSOR_SDM120_ENERGY_ACTIVE_IMPORT,
+	SENSOR_SDM120_ENERGY_ACTIVE_EXPORT,
+	SENSOR_SDM120_ENERGY_REACTIVE_IMPORT,
+	SENSOR_SDM120_ENERGY_REACTIVE_EXPORT,
+	SENSOR_SDM120_ENERGY_ACTIVE_TOTAL,
+	SENSOR_SDM120_ENERGY_REACTIVE_TOTAL,
+	SENSOR_SDM120_MAX
+};
+
+/** setup peripherals to communicate with electricity meter */
+void sensor_sdm120_setup(void);
+/** request measurement from electricity meter
+ *  @param[in] address electricity meter device address
+ *  @param[in] type measurement type to request
+ */
+void sensor_sdm120_measurement_request(uint8_t address, enum sensor_sdm120_measurement_type_t type);
+/** decode received measurement
+ *  @return decoded measurement (NaN if invalid or no new measurement has been received)
+ */
+float sensor_sdm120_measurement_decode(void);