feather-nrf52840: add support for saul_bat_voltage

boards/feather-nrf52840/Makefile.dep

@@ -1,5 +1,6 @@
 ifneq (,$(filter saul_default,$(USEMODULE)))
   USEMODULE += saul_gpio
+  USEMODULE += saul_bat_voltage
   USEMODULE += ws281x
 endif
 

boards/feather-nrf52840/Makefile.features

@@ -1,6 +1,7 @@
 CPU_MODEL = nrf52840xxaa
 
 # Put defined MCU peripherals here (in alphabetical order)
+FEATURES_PROVIDED += board_bat_voltage
 FEATURES_PROVIDED += periph_i2c
 FEATURES_PROVIDED += periph_spi
 FEATURES_PROVIDED += periph_uart

boards/feather-nrf52840/bat_voltage.c

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C)  2024 TU Dresden
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     boards_feather-nrf52840
+ * @ingroup     saul_bat_voltage
+ * @{
+ * @file
+ * @brief       Implementation of battery voltage convert function
+ *
+ * @author      Martine S. Lenders <[email protected]>
+ *
+ * @}
+ */
+
+#ifdef MODULE_SAUL_BAT_VOLTAGE
+#include "saul/bat_voltage.h"
+
+int16_t saul_bat_voltage_convert(int32_t adc_sample)
+{
+    /* See
+     * https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather/power-management-2
+     *
+     * but the reference voltage is actually 3.3V (determined empirically)...
+     * we return in millivolt so we set the reference voltage to 3300
+     * instead of 3.3 */
+    return (int16_t)((adc_sample * 2L * 3300L) / 1024L);
+}
+
+#endif /* MODULE_SAUL_BAT_VOLTAGE */

boards/feather-nrf52840/include/bat_voltage_params.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2024 TU Dresden
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     boards_feather-nrf52840
+ * @{
+ *
+ * @file
+ * @brief       Configuration of SAUL mapped battery voltage information
+ *
+ * @author      Martine S. Lenders <[email protected]>
+ */
+
+#ifndef BAT_VOLTAGE_PARAMS_H
+#define BAT_VOLTAGE_PARAMS_H
+
+#include "saul/bat_voltage.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief  Conversion function to convert ADC sample to battery voltage
+ *
+ * @param[in] adc_sample    The raw ADC sample.
+ *
+ * @return Voltage value for phydat.
+ */
+int16_t saul_bat_voltage_convert(int32_t adc_sample);
+
+/**
+ * @brief   Battery voltage configuration
+ */
+static const saul_bat_voltage_params_t saul_bat_voltage_params[] =
+{
+    {
+        .name = "BAT",
+        .phydat_scale = -3,
+        .line = ADC_LINE(5),
+        .res = ADC_RES_10BIT,
+        .convert = saul_bat_voltage_convert,
+    },
+};
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* BAT_VOLTAGE_PARAMS_H */
+/** @} */