current_sense_amplifier.h

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/*
 * Copyright (c) 2023 The ChromiumOS Authors
 *
 * SPDX-License-Identifier: Apache-2.0
 */
 
#ifndef ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_
#define ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_
 
#include <zephyr/drivers/adc.h>
#include <zephyr/drivers/gpio.h>
 
struct current_sense_amplifier_dt_spec {
        struct adc_dt_spec port;
        struct gpio_dt_spec power_gpio;
        uint32_t sense_milli_ohms;
        uint16_t sense_gain_mult;
        uint16_t sense_gain_div;
        uint16_t noise_threshold;
        int16_t zero_current_voltage_mv;
        enum adc_gain gain_extended_range;
        bool enable_calibration;
};

#define CURRENT_SENSE_AMPLIFIER_DT_SPEC_GET(node_id)                                               \
        {                                                                                          \
                .port = ADC_DT_SPEC_GET(node_id),                                                  \
                .power_gpio = GPIO_DT_SPEC_GET_OR(node_id, power_gpios, {0}),                      \
                .sense_milli_ohms = DT_PROP(node_id, sense_resistor_milli_ohms),                   \
                .sense_gain_mult = DT_PROP(node_id, sense_gain_mult),                              \
                .sense_gain_div = DT_PROP(node_id, sense_gain_div),                                \
                .noise_threshold = DT_PROP(node_id, zephyr_noise_threshold),                       \
                .zero_current_voltage_mv = DT_PROP(node_id, zero_current_voltage_mv),              \
                .gain_extended_range = DT_STRING_TOKEN_OR(node_id, gain_extended_range, 0xFF),     \
                .enable_calibration = DT_PROP_OR(node_id, enable_calibration, false),              \
        }

static inline void
current_sense_amplifier_scale_dt(const struct current_sense_amplifier_dt_spec *spec,
                                 int32_t *v_to_i)
{
        /* store in a temporary 64 bit variable to prevent overflow during calculation */
        int64_t tmp = *v_to_i;
 
        /* (INT32_MAX * 1000 * UINT16_MAX) < INT64_MAX
         * Therefore all multiplications can be done before divisions, preserving resolution.
         */
        tmp = tmp - spec->zero_current_voltage_mv;
        tmp = tmp * 1000 * spec->sense_gain_div / spec->sense_milli_ohms / spec->sense_gain_mult;
 
        *v_to_i = (int32_t)tmp;
}

static inline int32_t
current_sense_amplifier_scale_ua_dt(const struct current_sense_amplifier_dt_spec *spec,
                                    int32_t microvolts)
{
        int64_t temp = microvolts;
        /* Perform all multiplications first to limit rounding errors.
         * Micro-volts/milli-ohms would result in milli-amps, scale by factor of 1,000.
         * Proof that the following cannot overflow:
         *    (millivolts * micro_scale) * max_gain <= INT64_MAX
         *          (INT32_MAX * 1000) * UINT16_MAX <= INT64_MAX
         *                                   ~2**57 <= 2**63
         */
        int64_t scaled = temp * 1000 * spec->sense_gain_div;
        /* Perform final divisions */
        return scaled / spec->sense_gain_mult / spec->sense_milli_ohms;
}
 
#endif /* ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_ */