39 lines
1.3 KiB
C++
39 lines
1.3 KiB
C++
#pragma once
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#include <rusefi/rusefi_time_types.h>
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// custom start value could be useful for testing
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#ifndef WRAP_AROUND_INITIAL_UPPER
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#define WRAP_AROUND_INITIAL_UPPER 0
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#endif
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/**
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* Provide a 62-bit counter from a 32-bit counter source that wraps around.
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*
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* If you'd like it use it with a 16-bit counter, shift the source by 16 before passing it here.
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* This class is thread/interrupt-safe.
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*/
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struct WrapAround62 {
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uint64_t update(uint32_t source) {
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// Shift cannot be 31, as we wouldn't be able to tell if time is moving forward or
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// backward relative to m_upper. We do need to handle both directions as our
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// "thread" can be racing with other "threads" in sampling stamp and updating
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// m_upper.
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constexpr unsigned shift = 30;
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uint32_t upper = m_upper;
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uint32_t relative_unsigned = source - (upper << shift);
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upper += int32_t(relative_unsigned) >> shift;
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m_upper = upper;
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// Yes we could just do upper<<shift, but then the result would span both halves of
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// the 64-bit result. Doing it this way means we only operate on one half at a
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// time. Source will supply those bits anyways, so we don't need them from
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// upper...
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return (efitick_t(upper >> (32 - shift)) << 32) | source;
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}
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private:
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volatile uint32_t m_upper = WRAP_AROUND_INITIAL_UPPER;
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};
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