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https://github.com/mytechnotalent/Embedded-Hacking.git
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130 lines
4.3 KiB
C
130 lines
4.3 KiB
C
/**
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* @file ir.c
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* @brief Implementation of NEC IR receiver (decoder)
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* @author Kevin Thomas
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* @date 2025
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*
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* MIT License
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*
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* Copyright (c) 2025 Kevin Thomas
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "ir.h"
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#include "pico/stdlib.h"
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#include "pico/time.h"
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#include "hardware/gpio.h"
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static unsigned int ir_pin = 0;
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/**
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* @brief Wait for a GPIO pin to reach a given logic level
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*
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* Spins until the pin matches the requested level or a microsecond timeout
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* is exceeded. Returns the elapsed time in microseconds, or -1 on timeout.
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*
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* @param gpio GPIO pin to monitor
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* @param level Desired logic level (true = HIGH, false = LOW)
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* @param timeout_us Maximum wait in microseconds
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* @return int64_t Elapsed microseconds, or -1 on timeout
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*/
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static int64_t _wait_for_level(unsigned int gpio, bool level, uint32_t timeout_us) {
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absolute_time_t start = get_absolute_time();
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while (gpio_get(gpio) != level) {
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if (absolute_time_diff_us(start, get_absolute_time()) > (int64_t)timeout_us)
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return -1;
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}
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return absolute_time_diff_us(start, get_absolute_time());
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}
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/**
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* @brief Wait for the NEC 9 ms leader pulse and 4.5 ms space
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*
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* @return bool true if a valid leader was detected, false on timeout
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*/
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static bool _wait_leader(void) {
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if (_wait_for_level(ir_pin, 0, 150000) < 0) return false;
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int64_t t = _wait_for_level(ir_pin, 1, 12000);
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if (t < 8000 || t > 10000) return false;
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t = _wait_for_level(ir_pin, 0, 7000);
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if (t < 3500 || t > 5000) return false;
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return true;
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}
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/**
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* @brief Read a single NEC-encoded bit from the IR receiver
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*
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* Measures the mark/space timing and shifts the result into the
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* appropriate byte of the data array.
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*
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* @param data 4-byte array accumulating received bits
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* @param i Bit index (0-31)
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* @return bool true on success, false on timeout or protocol error
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*/
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static bool _read_nec_bit(uint8_t *data, int i) {
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if (_wait_for_level(ir_pin, 1, 1000) < 0) return false;
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int64_t t = _wait_for_level(ir_pin, 0, 2500);
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if (t < 200) return false;
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int byte_idx = i / 8;
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int bit_idx = i % 8;
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if (t > 1200) data[byte_idx] |= (1 << bit_idx);
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return true;
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}
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/**
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* @brief Read all 32 data bits of an NEC frame
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*
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* @param data 4-byte array filled with the received address and command
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* @return bool true if all 32 bits were read, false on timeout
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*/
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static bool _read_32_bits(uint8_t *data) {
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for (int i = 0; i < 32; ++i)
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if (!_read_nec_bit(data, i)) return false;
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return true;
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}
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/**
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* @brief Validate an NEC frame and extract the command byte
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*
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* Checks that the address and command pairs are bitwise-inverted.
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*
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* @param data 4-byte NEC frame (addr, ~addr, cmd, ~cmd)
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* @return int Command byte (0-255) on success, -1 on validation failure
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*/
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static int _validate_nec_frame(const uint8_t *data) {
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if ((uint8_t)(data[0] + data[1]) == 0xFF && (uint8_t)(data[2] + data[3]) == 0xFF)
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return data[2];
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return -1;
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}
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void ir_init(uint8_t pin) {
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ir_pin = pin;
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gpio_init(pin);
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gpio_set_dir(pin, GPIO_IN);
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gpio_pull_up(pin);
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}
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int ir_getkey(void) {
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if (!_wait_leader()) return -1;
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uint8_t data[4] = {0, 0, 0, 0};
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if (!_read_32_bits(data)) return -1;
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return _validate_nec_frame(data);
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}
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