Line data Source code
1 0 : /*
2 : * Copyright (c) 2023 The ChromiumOS Authors
3 : *
4 : * SPDX-License-Identifier: Apache-2.0
5 : */
6 :
7 : #ifndef ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_
8 : #define ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_
9 :
10 : #include <zephyr/drivers/adc.h>
11 : #include <zephyr/drivers/gpio.h>
12 :
13 0 : struct current_sense_amplifier_dt_spec {
14 0 : struct adc_dt_spec port;
15 0 : struct gpio_dt_spec power_gpio;
16 0 : uint32_t sense_milli_ohms;
17 0 : uint16_t sense_gain_mult;
18 0 : uint16_t sense_gain_div;
19 0 : uint16_t noise_threshold;
20 0 : int16_t zero_current_voltage_mv;
21 0 : enum adc_gain gain_extended_range;
22 0 : bool enable_calibration;
23 : };
24 :
25 : /**
26 : * @brief Get current sensor information from devicetree.
27 : *
28 : * This returns a static initializer for a @p current_sense_amplifier_dt_spec structure
29 : * given a devicetree node.
30 : *
31 : * @param node_id Devicetree node identifier.
32 : *
33 : * @return Static initializer for an current_sense_amplifier_dt_spec structure.
34 : */
35 1 : #define CURRENT_SENSE_AMPLIFIER_DT_SPEC_GET(node_id) \
36 : { \
37 : .port = ADC_DT_SPEC_GET(node_id), \
38 : .power_gpio = GPIO_DT_SPEC_GET_OR(node_id, power_gpios, {0}), \
39 : .sense_milli_ohms = DT_PROP(node_id, sense_resistor_milli_ohms), \
40 : .sense_gain_mult = DT_PROP(node_id, sense_gain_mult), \
41 : .sense_gain_div = DT_PROP(node_id, sense_gain_div), \
42 : .noise_threshold = DT_PROP(node_id, zephyr_noise_threshold), \
43 : .zero_current_voltage_mv = DT_PROP(node_id, zero_current_voltage_mv), \
44 : .gain_extended_range = DT_STRING_TOKEN_OR(node_id, gain_extended_range, 0xFF), \
45 : .enable_calibration = DT_PROP_OR(node_id, enable_calibration, false), \
46 : }
47 :
48 : /**
49 : * @brief Calculates the actual amperage from the measured voltage
50 : *
51 : * @param[in] spec current sensor specification from Devicetree.
52 : * @param[in,out] v_to_i Pointer to the measured voltage in millivolts on input, and the
53 : * corresponding scaled current value in milliamps on output.
54 : */
55 : static inline void
56 1 : current_sense_amplifier_scale_dt(const struct current_sense_amplifier_dt_spec *spec,
57 : int32_t *v_to_i)
58 : {
59 : /* store in a temporary 64 bit variable to prevent overflow during calculation */
60 : int64_t tmp = *v_to_i;
61 :
62 : /* (INT32_MAX * 1000 * UINT16_MAX) < INT64_MAX
63 : * Therefore all multiplications can be done before divisions, preserving resolution.
64 : */
65 : tmp = tmp - spec->zero_current_voltage_mv;
66 : tmp = tmp * 1000 * spec->sense_gain_div / spec->sense_milli_ohms / spec->sense_gain_mult;
67 :
68 : *v_to_i = (int32_t)tmp;
69 : }
70 :
71 : /**
72 : * @brief Calculates the actual amperage from the measured voltage
73 : *
74 : * @param spec Current sensor specification from Devicetree.
75 : * @param microvolts Measured voltage in microvolts.
76 : *
77 : * @return int32_t Corresponding scaled output current in microamps.
78 : */
79 : static inline int32_t
80 1 : current_sense_amplifier_scale_ua_dt(const struct current_sense_amplifier_dt_spec *spec,
81 : int32_t microvolts)
82 : {
83 : int64_t temp = microvolts;
84 : /* Perform all multiplications first to limit rounding errors.
85 : * Micro-volts/milli-ohms would result in milli-amps, scale by factor of 1,000.
86 : * Proof that the following cannot overflow:
87 : * (millivolts * micro_scale) * max_gain <= INT64_MAX
88 : * (INT32_MAX * 1000) * UINT16_MAX <= INT64_MAX
89 : * ~2**57 <= 2**63
90 : */
91 : int64_t scaled = temp * 1000 * spec->sense_gain_div;
92 : /* Perform final divisions */
93 : return scaled / spec->sense_gain_mult / spec->sense_milli_ohms;
94 : }
95 :
96 : #endif /* ZEPHYR_INCLUDE_DRIVERS_ADC_CURRENT_SENSE_AMPLIFIER_H_ */
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