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/** |
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* Check if button A,B,C state are pressed, include some software |
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* debouncing. |
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* |
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* Note: Only set bit when Button is state change from |
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* idle -> pressed. Press and hold only report 1 time, release |
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* won't report as well |
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* |
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* @return Bitmask of pressed buttons e.g If BUTTON_A is pressed |
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* bit 31 will be set. |
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*/ |
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uint32_t readPressedButtons(void) |
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{ |
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// must be exponent of 2 |
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enum { MAX_CHECKS = 8, SAMPLE_TIME = 10 }; |
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/* Array that maintains bounce status/, which is sampled |
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* 10 ms each. Debounced state is regconized if all the values |
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* of a button has the same value (bit set or clear) |
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*/ |
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static uint32_t lastReadTime = 0; |
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static uint32_t states[MAX_CHECKS] = { 0 }; |
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static uint32_t index = 0; |
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// Last Debounced state, used to detect changed |
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static uint32_t lastDebounced = 0; |
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// Too soon, nothing to do |
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if (millis() - lastReadTime < SAMPLE_TIME ) return 0; |
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lastReadTime = millis(); |
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// Take current read and masked with BUTTONs |
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// Note: Bitwise inverted since buttons are active (pressed) LOW |
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uint32_t debounced = ~(*portInputRegister(0)); |
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debounced &= (bit(BUTTON_A) | bit(BUTTON_B) | bit(BUTTON_C)); |
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// Copy current state into array |
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states[ (index & (MAX_CHECKS-1)) ] = debounced; |
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index++; |
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// Bitwise And all the state in the array together to get the result |
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// This means pin must stay at least MAX_CHECKS time to be realized as changed |
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for(int i=0; i<MAX_CHECKS; i++) |
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{ |
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debounced &= states[i]; |
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} |
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// result is button changed and current debounced is set |
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// Mean button is pressed (idle previously) |
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uint32_t result = (debounced ^ lastDebounced) & debounced; |
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lastDebounced = debounced; |
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return result; |
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} |
