62 lines
2.0 KiB
C
62 lines
2.0 KiB
C
/**
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* Copyright (c) 2021 pmarques-dev @ github
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <stdio.h>
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#include "pico/stdlib.h"
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#include "hardware/pio.h"
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#include "hardware/timer.h"
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#include "quadrature_encoder.pio.h"
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//
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// ---- quadrature encoder interface example
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//
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// the PIO program reads phase A/B of a quadrature encoder and increments or
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// decrements an internal counter to keep the current absolute step count
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// updated. At any point, the main code can query the current count by using
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// the quadrature_encoder_*_count functions. The counter is kept in a full
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// 32 bit register that just wraps around. Two's complement arithmetic means
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// that it can be interpreted as a 32-bit signed or unsigned value, and it will
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// work anyway.
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//
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// As an example, a two wheel robot being controlled at 100Hz, can use two
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// state machines to read the two encoders and in the main control loop it can
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// simply ask for the current encoder counts to get the absolute step count. It
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// can also subtract the values from the last sample to check how many steps
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// each wheel as done since the last sample period.
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//
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// One advantage of this approach is that it requires zero CPU time to keep the
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// encoder count updated and because of that it supports very high step rates.
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//
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int main() {
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int new_value, delta, old_value = 0;
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// Base pin to connect the A phase of the encoder.
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// The B phase must be connected to the next pin
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const uint PIN_AB = 10;
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stdio_init_all();
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PIO pio = pio0;
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const uint sm = 0;
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uint offset = pio_add_program(pio, &quadrature_encoder_program);
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quadrature_encoder_program_init(pio, sm, offset, PIN_AB, 0);
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while (1) {
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// note: thanks to two's complement arithmetic delta will always
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// be correct even when new_value wraps around MAXINT / MININT
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new_value = quadrature_encoder_get_count(pio, sm);
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delta = new_value - old_value;
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old_value = new_value;
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printf("position %8d, delta %6d\n", new_value, delta);
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sleep_ms(100);
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}
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}
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