Add basic ADC support

Planning on abstracting this behind hardware setup APIs, but this works
for a simple demo until then

CMakeLists.txt

@@ -9,10 +9,12 @@ target_sources(app PRIVATE
     core/main.c
     core/ble.c
     core/routine.c
+    core/hardware/adc.c
 )
 
 # User routines to compile
 target_sources(app PRIVATE
     routines/routine_list.c
     routines/input_echo.c
+    routines/photosensor.c
 )

boards/nrf52840dongle_nrf52840.overlay

@@ -0,0 +1,19 @@
+/ {
+    zephyr,user {
+        io-channels = <&adc 0>;
+    };
+};
+
+&adc {
+    #address-cells = <1>;
+    #size-cells = <0>;
+
+    channel@0 {
+        reg = <0>;
+        zephyr,gain = "ADC_GAIN_1_6";
+        zephyr,reference = "ADC_REF_INTERNAL";
+        zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+        zephyr,input-positive = <NRF_SAADC_AIN0>; /* P0.02 */
+        zephyr,resolution = <12>;
+    };
+};

core/hardware/adc.c

@@ -0,0 +1,75 @@
+#include <inttypes.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <zephyr/device.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/adc.h>
+#include <zephyr/kernel.h>
+
+/** Setup code referenced from Zephyr ADC example **/
+#if !DT_NODE_EXISTS(DT_PATH(zephyr_user)) || \
+	!DT_NODE_HAS_PROP(DT_PATH(zephyr_user), io_channels)
+#error "No suitable devicetree overlay specified"
+#endif
+
+#define DT_SPEC_AND_COMMA(node_id, prop, idx) \
+    ADC_DT_SPEC_GET_BY_IDX(node_id, idx),
+
+static const struct adc_dt_spec adc_channels[] = {
+    DT_FOREACH_PROP_ELEM(DT_PATH(zephyr_user), io_channels, DT_SPEC_AND_COMMA)
+};
+
+static int setup = 0;
+
+int
+adc_init()
+{
+    for (int i = 0; i < ARRAY_SIZE(adc_channels); i++) {
+        int err;
+        const struct adc_dt_spec *chan = &adc_channels[i];
+
+        if (!adc_is_ready_dt(chan)) {
+            return (-1);
+        }
+
+        err = adc_channel_setup_dt(chan);
+        if (err) {
+            return (err);
+        }
+    }
+
+    setup = 1;
+    return (0);
+}
+
+int
+adc_get_mv(int channel)
+{
+    uint16_t val_raw;
+    int32_t val_mv;
+    struct adc_sequence seq = {
+        .buffer = &val_raw,
+        .buffer_size = sizeof(val_raw)
+    };
+    const struct adc_dt_spec *chan;
+
+    if ((channel >= ARRAY_SIZE(adc_channels)) ||
+        (!setup)) {
+        return (INT32_MIN);
+    }
+
+    chan = &adc_channels[channel];
+    adc_sequence_init_dt(chan, &seq);
+
+    if (adc_read_dt(chan, &seq) < 0) {
+        return (INT32_MIN);
+    }
+
+    val_mv = (int32_t)val_raw;
+    if (adc_raw_to_millivolts_dt(chan, &val_mv)) {
+        return (INT32_MIN);
+    }
+
+    return (val_mv);
+}

core/hardware/adc.h

@@ -0,0 +1,11 @@
+#ifndef _ADC_H_
+#define _ADC_H_
+
+#include "includes/hardware/adc.h"
+
+/**
+ * @brief Initialize ADC hardware
+ */
+int adc_init(void);
+
+#endif /* _ADC_H_ */

core/main.c

@@ -5,10 +5,12 @@
 
 #include "core/ble.h"
 #include "core/routine.h"
+#include "core/hardware/adc.h"
 
 
 int main(void)
 {
+    adc_init();
     routine_init();
     ble_init();
 

includes/hardware/adc.h

@@ -0,0 +1,10 @@
+#ifndef _INCLUDES_HARDWARE_ADC_H_
+#define _INCLUDES_HARDWARE_ADC_H_
+
+/**
+ * @brief Read the ADC value from the given channel index. See "adc-channels" in
+ * your board overlay file.
+ */
+int adc_get_mv(int channel);
+
+#endif /* _INCLUDES_HARDWARE_ADC_H_ */

prj.conf

@@ -7,4 +7,7 @@ CONFIG_BT_GATT_DYNAMIC_DB=y
 
 CONFIG_HEAP_MEM_POOL_SIZE=1024
 
+CONFIG_ADC=y
+
 CONFIG_DEBUG=y
+CONFIG_DEBUG_OPTIMIZATIONS=y

routines/photosensor.c

@@ -0,0 +1,27 @@
+#include <zephyr/kernel.h>
+
+#include "includes/ble.h"
+#include "includes/routine.h"
+#include "includes/hardware/adc.h"
+
+routine_return_e
+photosensor()
+{
+    while (routine_status() == ROUTINE_STATUS_RUNNING) {
+        int32_t adc_mv = adc_get_mv(0);
+        char buf[16];
+        size_t print_len;
+
+        if (adc_mv == INT32_MIN) {
+            ble_set_telemetry_data("Reading failed", 14);
+        } else {
+            print_len = snprintk(buf, sizeof(buf), "%dmV", adc_mv);
+            ble_set_telemetry_data(buf, print_len);
+        }
+
+        routine_delay(500);
+        routine_yield();
+    }
+
+    return ROUTINE_RETURN_SUCCESS;
+}

routines/routine_list.c

@@ -4,8 +4,10 @@
 
 /** Extern all of your routines here so they can be included in the list **/
 extern routine_return_e input_echo();
+extern routine_return_e photosensor();
 
 const routine_listing_t routine_list[] = {
     { .entry = input_echo, .name = "Input Echo" },
+    { .entry = photosensor, .name = "Photosensor" },
     { NULL, NULL },
 };