Battery Voltage

Readout/monitor battery voltage and turn off in case it gets too low. Also make the voltage available via API.

Partly implements #34.

epicardium/modules/pmic.c

@@ -61,6 +61,18 @@ int pmic_read_amux(enum pmic_amux_signal sig, float *result)
 	/* Select the correct channel for this measurement.  */
 	MAX77650_setMUX_SEL(sig);
 
+	/*
+	 * According to the datasheet, the voltage will stabilize within 0.3us.
+	 * Just to be sure, we'll wait a little longer.  In the meantime,
+	 * release the I2C mutex.
+	 */
+	hwlock_release(HWLOCK_I2C);
+	vTaskDelay(pdMS_TO_TICKS(5));
+	ret = hwlock_acquire(HWLOCK_I2C, pdMS_TO_TICKS(100));
+	if (ret < 0) {
+		return ret;
+	}
+
 	uint16_t adc_data;
 	ADC_StartConvert(ADC_CH_0, 0, 0);
 	ADC_GetData(&adc_data);
@@ -75,9 +87,24 @@ int pmic_read_amux(enum pmic_amux_signal sig, float *result)
 	 * Convert value according to PMIC formulas (Table 7)
 	 */
 	switch (sig) {
+	case PMIC_AMUX_CHGIN_U:
+		*result = adc_voltage / 0.167f;
+		break;
+	case PMIC_AMUX_CHGIN_I:
+		*result = adc_voltage / 2.632f;
+		break;
 	case PMIC_AMUX_BATT_U:
 		*result = adc_voltage / 0.272f;
 		break;
+	case PMIC_AMUX_BATT_CHG_I:
+		*result = adc_voltage / 1.25f;
+		break;
+	case PMIC_AMUX_BATT_NULL_I:
+	case PMIC_AMUX_THM_U:
+	case PMIC_AMUX_TBIAS_U:
+	case PMIC_AMUX_AGND_U:
+		*result = adc_voltage;
+		break;
 	case PMIC_AMUX_SYS_U:
 		*result = adc_voltage / 0.26f;
 		break;