88b05f9391
Added component containg API that is able to correct raw ADC readings into a voltage in mV. Also provided a helper function that combines the process of getting the raw ADC1 reading then converting it to a voltage in mV. In doing so, the adc1_get_voltage() function of the ADC driver has been deprecated. Instead there is now adc1_get_raw to obtain the raw ADC1 reading, and adc1_to_voltage() that gets the raw reading and converts all in one function. Functions using the deprecated adc1_get_voltage() have also been updated to use adc1_get_raw(). Conversion is based on ADC characteristics. The characteristics are based on the ADC's v_ref, herefore the appropriate structure and functions have been provided to obtain the ADC characteristics. The existing ADC driver has also been modified by adding a function to route the internal ADC reference voltage to a GPIO allowing users to measure it manually. Relevant documentation has also been updated
112 lines
4.9 KiB
C
112 lines
4.9 KiB
C
// Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include <stdint.h>
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#include "driver/adc.h"
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#include "esp_adc_cal.h"
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static const esp_adc_cal_lookup_table_t *table_ptrs[4] = {&esp_adc_cal_table_atten_0,
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&esp_adc_cal_table_atten_1,
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&esp_adc_cal_table_atten_2,
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&esp_adc_cal_table_atten_3};
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uint32_t get_adc_vref_from_efuse()
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{
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//TODO: Replaced with read to eFuse once ATE confirms location of 5 bits
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return 0;
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}
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void esp_adc_cal_get_characteristics(uint32_t v_ref,
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adc_atten_t atten,
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adc_bits_width_t bit_width,
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esp_adc_cal_characteristics_t *chars)
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{
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chars->v_ref = v_ref;
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chars->table = table_ptrs[atten];
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chars->bit_width = bit_width;
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if (v_ref >= ADC_CAL_LOW_V_REF) {
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chars->gain = ((chars->v_ref - ADC_CAL_LOW_V_REF)
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* chars->table->gain_m)
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+ chars->table->gain_c;
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chars->offset = (((chars->v_ref - ADC_CAL_LOW_V_REF)
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* chars->table->offset_m)
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+ chars->table->offset_c
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+ ((1 << ADC_CAL_OFFSET_SCALE) / 2))
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>> ADC_CAL_OFFSET_SCALE; //Bit shift to cancel 2^10 multiplier
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chars->ideal_offset = (((ADC_CAL_IDEAL_V_REF - ADC_CAL_LOW_V_REF)
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* chars->table->offset_m)
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+ chars->table->offset_c
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+ ((1 << ADC_CAL_OFFSET_SCALE) / 2)) //Rounding
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>> ADC_CAL_OFFSET_SCALE;
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} else { //For case where v_ref is smaller than low bound resulting in negative
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chars->gain = chars->table->gain_c
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- ((ADC_CAL_LOW_V_REF - chars->v_ref)
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* chars->table->gain_m);
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chars->offset = (chars->table->offset_c
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- ((chars->v_ref - ADC_CAL_LOW_V_REF)
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* chars->table->offset_m)
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+ ((1 << ADC_CAL_OFFSET_SCALE) / 2)) //Rounding
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>> ADC_CAL_OFFSET_SCALE; //Bit shift to cancel 2^10 multiplier
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chars->ideal_offset = (chars->table->offset_c
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- ((ADC_CAL_IDEAL_V_REF - ADC_CAL_LOW_V_REF)
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* chars->table->offset_m)
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+ ((1 << ADC_CAL_OFFSET_SCALE) / 2)) //Rounding
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>> ADC_CAL_OFFSET_SCALE;
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}
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}
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static uint32_t esp_adc_cal_interpolate_round(uint32_t lower, uint32_t upper,
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uint32_t step, uint32_t point)
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{
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//Interpolate 'point' between 'lower' and 'upper' seperated by 'step'
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return ((lower * step) - (lower * point) + (upper * point) + (step / 2)) / step;
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}
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uint32_t esp_adc_cal_raw_to_voltage(uint32_t adc,
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const esp_adc_cal_characteristics_t *chars)
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{
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//Scale ADC to 12 bit width (0 to 4095)
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adc <<= (ADC_WIDTH_12Bit - chars->bit_width);
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uint32_t i = (adc >> chars->table->bit_shift); //find index for lut voltages
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//Refernce LUT to obtain voltage using index
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uint32_t voltage = esp_adc_cal_interpolate_round(chars->table->voltage[i],
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chars->table->voltage[i + 1],
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(1 << chars->table->bit_shift),
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adc - (i << chars->table->bit_shift));
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/*
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* Apply Gain, scaling(bit shift) and offset to interpolated voltage
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* v_true = (((v_id - off_id)*gain)*scaling) + off_true
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*/
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if (voltage > chars->ideal_offset) {
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voltage = (voltage - chars->ideal_offset) * chars->gain;
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voltage += (1 << ADC_CAL_GAIN_SCALE) / 2; //For rounding when scaled
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voltage >>= ADC_CAL_GAIN_SCALE;
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voltage += chars->offset;
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} else { //For case where voltage is less than ideal offset leading to negative value
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voltage = ((chars->ideal_offset - voltage) * chars->gain);
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voltage += (1 << ADC_CAL_GAIN_SCALE) / 2; //For rounding when scaled
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voltage >>= ADC_CAL_GAIN_SCALE;
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voltage = chars->offset - voltage;
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}
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return voltage;
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}
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uint32_t adc1_to_voltage(adc1_channel_t channel, const esp_adc_cal_characteristics_t *chars)
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{
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return esp_adc_cal_raw_to_voltage((uint32_t)adc1_get_raw(channel), chars);
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}
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