From 5a39bcae843b2f5545f0660053f925273adbbdd0 Mon Sep 17 00:00:00 2001
From: "Peter A. Bigot" <pab@pabigot.com>
Date: Mon, 29 Jul 2019 09:35:33 -0500
Subject: [PATCH] drivers/adc: provide API to access reference voltage

Required for any real-world use of ADC_REF_INTERNAL.

Relates-to: issue #11922
Signed-off-by: Peter A. Bigot <pab@pabigot.com>
---
 drivers/adc/adc_nrfx_adc.c   |  1 +
 drivers/adc/adc_nrfx_saadc.c |  1 +
 include/drivers/adc.h        | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/drivers/adc/adc_nrfx_adc.c b/drivers/adc/adc_nrfx_adc.c
index de607a158a6..5fbed6d9aa8 100644
--- a/drivers/adc/adc_nrfx_adc.c
+++ b/drivers/adc/adc_nrfx_adc.c
@@ -274,6 +274,7 @@ static const struct adc_driver_api adc_nrfx_driver_api = {
 #ifdef CONFIG_ADC_ASYNC
 	.read_async    = adc_nrfx_read_async,
 #endif
+	.ref_internal  = 1200,
 };
 
 #ifdef CONFIG_ADC_0
diff --git a/drivers/adc/adc_nrfx_saadc.c b/drivers/adc/adc_nrfx_saadc.c
index 8bda534e2ce..516771f2ce5 100644
--- a/drivers/adc/adc_nrfx_saadc.c
+++ b/drivers/adc/adc_nrfx_saadc.c
@@ -406,6 +406,7 @@ static const struct adc_driver_api adc_nrfx_driver_api = {
 #ifdef CONFIG_ADC_ASYNC
 	.read_async    = adc_nrfx_read_async,
 #endif
+	.ref_internal  = 600,
 };
 
 #ifdef CONFIG_ADC_0
diff --git a/include/drivers/adc.h b/include/drivers/adc.h
index 467ae82def7..1bb85220bdf 100644
--- a/include/drivers/adc.h
+++ b/include/drivers/adc.h
@@ -302,6 +302,7 @@ struct adc_driver_api {
 #ifdef CONFIG_ADC_ASYNC
 	adc_api_read_async    read_async;
 #endif
+	u16_t ref_internal;	/* mV */
 };
 
 /**
@@ -394,6 +395,23 @@ static inline int z_impl_adc_read_async(struct device *dev,
 }
 #endif /* CONFIG_ADC_ASYNC */
 
+/**
+ * @brief Get the internal reference voltage.
+ *
+ * Returns the voltage corresponding to @ref ADC_REF_INTERNAL,
+ * measured in millivolts.
+ *
+ * @return a positive value is the reference voltage value.  Returns
+ * zero if reference voltage information is not available.
+ */
+static inline u16_t adc_ref_internal(struct device *dev)
+{
+	const struct adc_driver_api *api =
+				(const struct adc_driver_api *)dev->driver_api;
+
+	return api->ref_internal;
+}
+
 #include <syscalls/adc.h>
 
 /**