cpu/nrf52: add SAUL driver for VDDH sensor

cpu/nrf52/Makefile.dep

@@ -22,5 +22,9 @@ ifneq (,$(filter periph_uart_nonblocking,$(USEMODULE)))
   USEMODULE += tsrb
 endif
 
+ifneq (,$(filter saul_nrf_vddh,$(USEMODULE)))
+  FEATURES_REQUIRED += periph_adc
+endif
+
 include $(RIOTCPU)/nrf5x_common/Makefile.dep
 include $(RIOTCPU)/cortexm_common/Makefile.dep

drivers/saul/init_devs/auto_init_saul_nrf_vddh.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2021 ML!PA Consulting GmbH
+ *
+ * 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     sys_auto_init_saul
+ * @{
+ *
+ * @file
+ * @brief       Auto initialization of internal voltage sensor directly mapped to SAUL reg
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ *
+ * @}
+ */
+
+#include "cpu.h"
+#include "log.h"
+#include "saul_reg.h"
+#include "saul/periph.h"
+#include "periph/adc.h"
+
+static int _read_voltage(const void *dev, phydat_t *res)
+{
+    (void)dev;
+
+    /* GPIO reference voltage / external output supply voltage in high voltage mode */
+    const uint8_t vref_deci_volt[] = { 18, 21, 24, 27, 30, 33, 0, 18 };
+    uint8_t idx = NRF_UICR->REGOUT0 & UICR_REGOUT0_VOUT_Msk;
+
+    int raw = adc_sample(NRF52_VDDHDIV5, ADC_RES_12BIT) * 5 * vref_deci_volt[idx] * 100;
+    res->val[0] = raw >> 12;
+    res->unit = UNIT_V;
+    res->scale = -3;
+
+    return 1;
+}
+
+static saul_driver_t nrf_vddh_saul_driver = {
+    .read = _read_voltage,
+    .write = saul_notsup,
+    .type = SAUL_SENSE_VOLTAGE,
+};
+
+void auto_init_nrf_vddh(void)
+{
+    static saul_reg_t saul_reg_entry = {
+        .dev = NULL,
+        .name = "NRF_VDDH",
+        .driver = &nrf_vddh_saul_driver,
+    };
+
+    adc_init(NRF52_VDDHDIV5);
+
+    /* add to registry */
+    saul_reg_add(&(saul_reg_entry));
+}

drivers/saul/init_devs/init.c

@@ -43,6 +43,10 @@ void saul_init_devs(void)
         extern void auto_init_nrf_temperature(void);
         auto_init_nrf_temperature();
     }
+    if (IS_USED(MODULE_SAUL_NRF_VDDH)) {
+        extern void auto_init_nrf_vddh(void);
+        auto_init_nrf_vddh();
+    }
     if (IS_USED(MODULE_AD7746)) {
         extern void auto_init_ad7746(void);
         auto_init_ad7746();

makefiles/pseudomodules.inc.mk

@@ -121,6 +121,7 @@ PSEUDOMODULES += saul_adc
 PSEUDOMODULES += saul_default
 PSEUDOMODULES += saul_gpio
 PSEUDOMODULES += saul_nrf_temperature
+PSEUDOMODULES += saul_nrf_vddh
 PSEUDOMODULES += saul_pwm
 PSEUDOMODULES += scanf_float
 PSEUDOMODULES += sched_cb