67 lines
2.9 KiB
C++
67 lines
2.9 KiB
C++
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/* debounce() function
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Debounce uses multiple samples to debounces switch states,
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where each sample contains the switch states for a row of switches, one bit per switch.
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Debounce uses Dr. Marty's debounce algorithm from
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http://drmarty.blogspot.com.br/2009/05/best-switch-debounce-routine-ever.html
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I2C and TWI protocols do not include any Packet Error Checking (PEC).
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The goal of Marty's debounce routine is to reject spurious signals,
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which is useful when connecting split keyboards with a cable using I2C or TWI.
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Was tested on split keyboard with 3-meter long telephone wire to I/O expander
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Dr. Marty's debounce algorithm:
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Periodically read samples and update the state when a number consecutive sample bits are equal.
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Output from keybrd/examples/debounce_unit_test.cpp with SAMPLE_COUNT 4:
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button pressed: 100000001111111110000
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bouncy signal: 100001001111011110000
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debounced signal: 000000000001111111110
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isFallingEdge: 000000000000000000001
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isRisingEdge: 000000000001000000000
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There is a latency equal to SAMPLE_COUNT, between button press and debounced signal.
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samples[SAMPLE_COUNT] is a ring buffer. samplesIndex is it's current write index.
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SAMPLE_COUNT is the number of consecutive equal samples needed to debounce.
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SAMPLE_COUNT is a macro because it defines samples[SAMPLE_COUNT] array size at compile time.
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SAMPLE_COUNT should be at lease 1.
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SAMPLE_COUNT = 4 is very reliable for a keyboard.
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Keyboards with a long I2C wire or in environment with strong electromagnetic interference (EMI)
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may need a larger SAMPLE_COUNT for reliability.
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*/
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#include "Debouncer_4Samples.h"
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/* debounce() sets debounced and returns debouncedChanged. All variables are bitwise.
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For parameters, 1 means pressed, 0 means released.
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For return, 1 means debounced changed.
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*/
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uint8_t Debouncer_4Samples::debounce(const uint8_t rawSignal, uint8_t& debounced)
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{
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uint8_t previousDebounced; //bitwise, 1 means pressed, 0 means released
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uint8_t all_1 = ~0; //bitwise
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uint8_t all_0 = 0; //bitwise
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samples[samplesIndex] = rawSignal; //insert rawSignal into samples[] ring buffer
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if (++samplesIndex >= SAMPLE_COUNT) //if end of ring buffer
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{
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samplesIndex = 0; //wrap samplesIndex to beginning of ring buffer
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}
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for (uint8_t j = 0; j < SAMPLE_COUNT; j++) //traverse the sample[] ring buffer
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{
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all_1 &= samples[j]; //1 if all samples are 1
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all_0 |= samples[j]; //0 if all samples are 0
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}
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previousDebounced = debounced;
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// update debounced if all the samples agree with one another
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// if all samples=1 then debounced=1
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// elseif all samples=0 then debounced=0
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// else debounced=previousDebounced i.e. no change
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debounced = all_1 | (all_0 & previousDebounced);
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return debounced xor previousDebounced;
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}
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