drivers: sensor: ina237: add shunt voltage support

Add ability to retrieve the shunt voltage if the end user wants to do
the power calculation manually to handle negative power values.

Signed-off-by: Eric Holmberg <eric.holmberg@northriversystems.co.nz>

drivers/sensor/ina23x/Kconfig

@@ -26,6 +26,20 @@ config INA237
 	help
 	  Enable driver for INA237.
 
+config INA237_VSHUNT
+	bool "INA237 VShunt Measurement Enable"
+	depends on DT_HAS_TI_INA237_ENABLED
+	help
+	  Enable shunt voltage measurement for INA237.
+
+	  This is the actual shunt voltage measured which is scaled within the
+	  INA237 based upon the SHUNT_CAL register.  This value is useful for
+	  looking at measurement noise or debugging the SHUNT_CAL value.
+
+	  Note that enabling this option requires an extra I2C read when
+	  SENSOR_CHAN_ALL is selected, so only enable if the shunt voltage
+	  measurement is required.
+
 config INA230_TRIGGER
 	bool "INA230 trigger mode"
 	depends on INA230

drivers/sensor/ina23x/ina237.c

@@ -65,6 +65,18 @@ static int ina237_channel_get(const struct device *dev, enum sensor_channel chan
 			INA237_POWER_TO_uW((uint64_t)data->power * config->current_lsb));
 		break;
 
+#ifdef CONFIG_INA237_VSHUNT
+	case SENSOR_CHAN_VSHUNT:
+		if (config->config & INA237_CFG_HIGH_PRECISION) {
+			/* high-resolution mode - 1.25 uV/bit, sensor value is in mV */
+			micro_s32_to_sensor_value(val, data->shunt_voltage * 1250);
+		} else {
+			/* standard-resolution - 5 uV/bit -> nano-volts */
+			micro_s32_to_sensor_value(val, data->shunt_voltage * 5000);
+		}
+		break;
+#endif /* CONFIG_INA237_VSHUNT */
+
 	case SENSOR_CHAN_DIE_TEMP:
 		micro_s32_to_sensor_value(val, INA237_DIETEMP_TO_uDegC(data->die_temp));
 		break;
@@ -165,6 +177,16 @@ static int ina237_read_data(const struct device *dev)
 		}
 	}
 
+#ifdef CONFIG_INA237_VSHUNT
+	if ((data->chan == SENSOR_CHAN_ALL) || (data->chan == SENSOR_CHAN_VSHUNT)) {
+		ret = ina23x_reg_read_16(&config->bus, INA237_REG_SHUNT_VOLT, &data->shunt_voltage);
+		if (ret < 0) {
+			LOG_ERR("Failed to read shunt voltage");
+			return ret;
+		}
+	}
+#endif /* CONFIG_INA237_VSHUNT */
+
 	return 0;
 }
 
@@ -179,7 +201,11 @@ static int ina237_sample_fetch(const struct device *dev, enum sensor_channel cha
 	struct ina237_data *data = dev->data;
 
 	if (chan != SENSOR_CHAN_ALL && chan != SENSOR_CHAN_VOLTAGE && chan != SENSOR_CHAN_CURRENT &&
-	    chan != SENSOR_CHAN_POWER && chan != SENSOR_CHAN_DIE_TEMP) {
+		chan != SENSOR_CHAN_POWER &&
+#ifdef CONFIG_INA237_VSHUNT
+		chan != SENSOR_CHAN_VSHUNT &&
+#endif /* CONFIG_INA237_VSHUNT */
+		chan != SENSOR_CHAN_DIE_TEMP) {
 		return -ENOTSUP;
 	}
 

drivers/sensor/ina23x/ina237.h

@@ -43,6 +43,9 @@ struct ina237_data {
 	uint16_t bus_voltage;
 	uint32_t power;
 	int16_t die_temp;
+#ifdef CONFIG_INA237_VSHUNT
+	int16_t shunt_voltage;
+#endif
 	enum sensor_channel chan;
 	struct ina23x_trigger trigger;
 };

include/zephyr/drivers/sensor.h

@@ -124,6 +124,10 @@ enum sensor_channel {
 
 	/** Voltage, in volts **/
 	SENSOR_CHAN_VOLTAGE,
+
+	/** Current Shunt Voltage in milli-volts **/
+	SENSOR_CHAN_VSHUNT,
+
 	/** Current, in amps **/
 	SENSOR_CHAN_CURRENT,
 	/** Power in watts **/

tests/drivers/sensor/ina237/prj.conf

@@ -10,5 +10,6 @@ CONFIG_I2C_EMUL=y
 CONFIG_I2C_LOG_LEVEL_DBG=y
 
 CONFIG_INA237=y
+CONFIG_INA237_VSHUNT=y
 
 CONFIG_CBPRINTF_FP_SUPPORT=y

tests/drivers/sensor/ina237/src/ina237_test.c

@@ -197,6 +197,51 @@ static void test_temperature(struct ina237_fixture *fixture)
 	}
 }
 
+static void test_vshunt(struct ina237_fixture *fixture)
+{
+	zassert_not_null(fixture->mock);
+
+	/* 16-bit signed value for voltage register (but always positive) 3.125 mV/bit */
+	const int16_t vshunt_reg_vectors[] = {
+		32767,	/* maximum shunt voltage of 163.84 mV or 40.96 mV */
+		27200,
+		1000,
+		100,
+		1,
+		0,
+		-1,
+		-100,
+		-1000,
+		-32768,	/* minimum shunt voltage of -163.84 mV or -40.96 mV */
+	};
+
+	for (int idx = 0; idx < ARRAY_SIZE(vshunt_reg_vectors); idx++) {
+		struct sensor_value sensor_val;
+
+		ina237_mock_set_register(fixture->mock->data, INA237_REG_SHUNT_VOLT,
+			vshunt_reg_vectors[idx]);
+
+		/* Verify sensor value is correct */
+		zassert_ok(sensor_sample_fetch_chan(fixture->dev, SENSOR_CHAN_VSHUNT));
+		zassert_ok(sensor_channel_get(fixture->dev, SENSOR_CHAN_VSHUNT, &sensor_val));
+
+		double vshunt_actual_mV = sensor_value_to_double(&sensor_val);
+		double vshunt_expected_mV = vshunt_reg_vectors[idx];
+
+		if (fixture->config & INA237_CFG_HIGH_PRECISION) {
+			/* High precision mode - 1.25 uV/bit = 1250 nV/bit*/
+			vshunt_expected_mV *= 1000 * 1.250e-6;
+		} else {
+			/* Standard precision mode - 5 uV/bit = 5000 nV/bit */
+			vshunt_expected_mV *= 1000 * 5e-6;
+		}
+
+		zexpect_within(vshunt_expected_mV, vshunt_actual_mV, 1e-9,
+			"For %d, Expected %.6f mV, got %.6f mV", vshunt_reg_vectors[idx],
+			vshunt_expected_mV, vshunt_actual_mV);
+	}
+}
+
 /* Create a test fixture for each enabled ina237 device node */
 #define DT_DRV_COMPAT ti_ina237
 #define INA237_FIXTURE_ENTRY(inst) \
@@ -219,6 +264,7 @@ static struct ina237_fixture fixtures[] = {
 	ZTEST(ina237_##inst, test_bus_voltage) { test_bus_voltage(&fixtures[inst]); } \
 	ZTEST(ina237_##inst, test_power) { test_power(&fixtures[inst]); } \
 	ZTEST(ina237_##inst, test_temperature) { test_temperature(&fixtures[inst]); } \
+	ZTEST(ina237_##inst, test_vshunt) { test_vshunt(&fixtures[inst]); } \
 	ZTEST_SUITE(ina237_##inst, NULL, NULL, NULL, NULL, NULL);
 
 DT_INST_FOREACH_STATUS_OKAY(INA237_TESTS)