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// Copyright 2021 The Pigweed Authors
//
// 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
//
// https://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.
#pragma once
#include "pw_analog/analog_input.h"
#include "pw_chrono/system_clock.h"
#include "pw_result/result.h"
#include "pw_status/try.h"
namespace pw::analog {
/// The common interface for obtaining voltage samples in microvolts. This
/// interface represents a single voltage input or channel. Users will need to
/// supply their own ADC driver implementation in order to provide the reference
/// voltages and to configure and enable the ADC peripheral where needed. Users
/// are responsible for managing multi-threaded access to the ADC driver if the
/// ADC services multiple channels.
class MicrovoltInput : public AnalogInput {
public:
/// Specifies the maximum and minimum microvolt range the analog input can
/// measure. The reference voltage difference cannot be bigger than
/// `sizeof(int32_t)` which should be just above 2000V. These values do not
/// change at run time. Inversion of `min` or `max` is supported.
struct References {
/// Microvolts at `AnalogInput::Limits::max`.
int32_t max_voltage_uv;
/// Microvolts at `AnalogInput::Limits::min`.
int32_t min_voltage_uv;
};
~MicrovoltInput() override = default;
/// Blocks until the specified timeout duration has elapsed or the voltage
/// sample has been returned, whichever comes first.
///
/// This method is thread-safe.
///
/// @returns
/// * A voltage sample in microvolts (uV) on success.
/// * @pw_status{RESOURCE_EXHAUSTED} - ADC peripheral in use.
/// * @pw_status{DEADLINE_EXCEEDED} - Timed out waiting for a sample.
/// * Other statuses left up to the implementer.
Result<int32_t> TryReadMicrovoltsFor(chrono::SystemClock::duration timeout) {
return TryReadMicrovoltsUntil(
chrono::SystemClock::TimePointAfterAtLeast(timeout));
}
/// Blocks until the deadline time has been reached or the voltage sample has
/// been returned, whichever comes first.
///
/// This method is thread-safe.
///
/// @returns
/// * A voltage sample in microvolts (uV) on success.
/// * @pw_status{RESOURCE_EXHAUSTED} - ADC peripheral in use.
/// * @pw_status{DEADLINE_EXCEEDED} - Timed out waiting for a sample.
/// * Other statuses left up to the implementer.
Result<int32_t> TryReadMicrovoltsUntil(
chrono::SystemClock::time_point deadline) {
PW_TRY_ASSIGN(const int32_t sample, TryReadUntil(deadline));
const References reference = GetReferences();
const AnalogInput::Limits limits = GetLimits();
constexpr int64_t kMaxReferenceDiffUv = std::numeric_limits<int32_t>::max();
if (std::abs(static_cast<int64_t>(reference.max_voltage_uv) -
static_cast<int64_t>(reference.min_voltage_uv)) >
kMaxReferenceDiffUv) {
return pw::Status::Internal();
}
return (((static_cast<int64_t>(sample) - static_cast<int64_t>(limits.min)) *
(reference.max_voltage_uv - reference.min_voltage_uv)) /
(limits.max - limits.min)) +
reference.min_voltage_uv;
}
private:
// Returns the reference voltage needed to calculate the voltage.
// These values do not change at run time.
virtual References GetReferences() const = 0;
};
} // namespace pw::analog
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