mirror of https://github.com/rusefi/rusefi.git
72 lines
2.1 KiB
C++
72 lines
2.1 KiB
C++
/**
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* @file efilib2.cpp
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*
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* @date Apr 14, 2014
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* @author Andrey Belomutskiy, (c) 2012-2014
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*/
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#include "efilib2.h"
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/**
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* The main use-case of this class is to keep track of a 64-bit global number of CPU ticks from reset.
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*
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* stm32f4 hardware has a 32-bit Cycle Count Register (CYCCNT), which is incremented with every CPU cycle.
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* With 32 bits and 168MHz speed this counter overflows every 4B/168M = 23 seconds. The job of this class is to
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* keep track of the current CYCCNT value, detect these overflows, and provide a nice,
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* clean 64 bit global cycle counter.
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*
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* In order for this to function, it's your responsibility to invoke offer() method at least once a second.
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*/
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Overflow64Counter::Overflow64Counter() {
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state.highBits = 0;
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state.lowBits = 0;
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}
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/**
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* in order to have atomic writes this should be invoked within a critical section
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*/
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void updateAndSet(State64 *state, uint32_t value) {
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if (value < state->lowBits) {
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// new value less than previous value means there was an overflow in that 32 bit counter
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state->highBits += 0x100000000LL;
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}
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state->lowBits = value;
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}
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uint64_t Overflow64Counter::update(uint32_t value) {
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updateAndSet(&state, value);
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return state.highBits + state.lowBits;
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}
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// todo: make this a macro? always inline?
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uint64_t Overflow64Counter::get() {
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/**
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* this method is lock-free and thread-safe, that's because the 'update' method
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* is atomic with a critical zone requirement.
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*
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* http://stackoverflow.com/questions/5162673/how-to-read-two-32bit-counters-as-a-64bit-integer-without-race-condition
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*/
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// these are local copies for thread-safery
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// todo: this is still not atomic, so technically not thread safe.
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uint64_t localH;
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uint32_t localLow;
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while (true) {
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localH = state.highBits;
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localLow = state.lowBits;
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uint64_t localH2 = state.highBits;
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if (localH == localH2)
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break;
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}
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/**
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* We need to take current counter after making a local 64 bit snapshot
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*/
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uint32_t value = GET_TIMESTAMP();
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if (value < localLow) {
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// new value less than previous value means there was an overflow in that 32 bit counter
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localH += 0x100000000LL;
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}
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return localH + value;
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}
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