File content as of revision 189:f392fc9709a3:

/* mbed Microcontroller Library
 * Copyright (c) 2006-2013 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "mbed_assert.h"
#include "analogin_api.h"
#include "cmsis.h"
#include "pinmap.h"

#define ANALOGIN_MEDIAN_FILTER      1
#define ADC_10BIT_RANGE             0x3FF
#define ADC_RANGE    ADC_10BIT_RANGE

static const PinMap PinMap_ADC[] = {
    {P0_1, ADC0_0, 4},
    {P0_2, ADC0_0, 8},
    {P0_3, ADC0_0, 16},
    {P0_4, ADC0_0, 32},
    {P0_5, ADC0_0, 64},
    {P0_6, ADC0_0, 128},
#ifndef TARGET_NRF51_DONGLE
    {P0_26, ADC0_0, 1},
    {P0_27, ADC0_0, 2},
#endif
    {NC, NC, 0}
};

void analogin_init(analogin_t *obj, PinName pin)
{
    int analogInputPin = 0;
    const PinMap *map  = PinMap_ADC;

    obj->adc = (ADCName)pinmap_peripheral(pin, PinMap_ADC); //(NRF_ADC_Type *)
    MBED_ASSERT(obj->adc != (ADCName)NC);

    while (map->pin != NC) {
        if (map->pin == pin) {
            analogInputPin = map->function;
            break;
        }
        map++;
    }
    obj->adc_pin = (uint8_t)analogInputPin;

    NRF_ADC->ENABLE = ADC_ENABLE_ENABLE_Enabled;
    NRF_ADC->CONFIG = (ADC_CONFIG_RES_10bit << ADC_CONFIG_RES_Pos) |
                      (ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos) |
                      (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos) |
                      (analogInputPin << ADC_CONFIG_PSEL_Pos) |
                      (ADC_CONFIG_EXTREFSEL_None << ADC_CONFIG_EXTREFSEL_Pos);
}

uint16_t analogin_read_u16(analogin_t *obj)
{
    NRF_ADC->CONFIG     &= ~ADC_CONFIG_PSEL_Msk;
    NRF_ADC->CONFIG     |= obj->adc_pin << ADC_CONFIG_PSEL_Pos;
    NRF_ADC->EVENTS_END  = 0;
    NRF_ADC->TASKS_START = 1;

    while (!NRF_ADC->EVENTS_END) {
    }

    return (uint16_t)NRF_ADC->RESULT; // 10 bit
}

float analogin_read(analogin_t *obj)
{
    uint16_t value = analogin_read_u16(obj);
    return (float)value * (1.0f / (float)ADC_RANGE);
}