lezyne-rear-light-firmware/main.c

/**
 * @file main.c
 * @brief Bike rear light implementation for ATTINY202.
 *
 */

#include <stdint.h>
#include <stdbool.h>
#include <avr/io.h>
#include <util/delay.h>

/** @defgroup LED_Masks LED bitmasks for PORTA
 *  @{
 */
#define PA1_SET_MASK 0x02 ///< LED 1–2
#define PA2_SET_MASK 0x04 ///< LED 3–6
#define PA3_SET_MASK 0x08 ///< LED 7–8
#define PA6_SET_MASK 0x40 ///< Green LED
#define PA7_SET_MASK 0x80 ///< Red LED
/** @} */

/** @brief Main loop delay in ms (system tick). */
#define MAIN_LOOP_SLEEP 10U

/** @brief Convert milliseconds to system ticks (integer division). */
#define MS_TO_TICKS(ms) ((ms) / MAIN_LOOP_SLEEP)

/** @brief Global flag: enable or disable LED output. */
volatile bool bLedEnabled = true;

// Function forward declarations
void blinkLed(void);
static inline void leds_off(void);

/**
 * @brief Main entry point.
 *
 * Initializes I/O ports and runs the main loop, periodically calling @ref blinkLed().
 *
 * @return never returns
 */
int main(void)
{
    // --- configure LED pins as outputs ---
    VPORTA.DIR = (PA1_SET_MASK | PA2_SET_MASK | PA3_SET_MASK |
                  PA6_SET_MASK | PA7_SET_MASK);

    // --- ensure all LEDs off at startup ---
    leds_off();
    VPORTA.OUT &= (uint8_t)~(PA6_SET_MASK | PA7_SET_MASK);

    while (true)
    {
        // TODO: add status LED handling if needed
        // VPORTA.OUT ^= PA6_SET_MASK; // toggle green LED
        // VPORTA.OUT ^= PA7_SET_MASK; // toggle red LED

        blinkLed();

        _delay_ms(MAIN_LOOP_SLEEP);
    }
}

/**
 * @brief Switch off all controlled LEDs (PA1, PA2, PA3).
 *
 * @note Declared inline for speed (single instruction sequence).
 */
static inline void leds_off(void)
{
    VPORTA.OUT &= (uint8_t)~(PA1_SET_MASK | PA2_SET_MASK | PA3_SET_MASK);
}

/**
 * @brief LED blink state machine.
 *
 * Implements the following repeating sequence (non-blocking):
 *
 * Normal cycle:
 *   - Step 0:  all off, wait 250 ms
 *   - Step 2:  LED 1–2 + 7–8 on, wait 50 ms
 *   - Step 5:  all off, wait 100 ms
 *   - Step 7:  LED 1–2 + 7–8 on, wait 50 ms
 *   - Step 10: all off, wait 250 ms
 *   - Step 12: LED 3–6 on, wait 50 ms
 *   - Step 14: all off, wait 100 ms
 *   - Step 16: LED 3–6 on, wait 50 ms
 *   - Step 18: all off, wait 250 ms → restart
 *
 * Special behavior:
 *   - Every 3rd cycle, after step 18, all LEDs (PA1, PA2, PA3) are switched on for 250 ms.
 *
 * Timing is based on @ref MAIN_LOOP_SLEEP ticks.
 *
 * @note Must be called periodically every 10 ms from the main loop.
 * @note Depends on global flag ::bLedEnabled. If false, does nothing.
 */
void blinkLed(void)
{
    // --- precomputed constants (compile-time) ---
    const uint8_t T50 = MS_TO_TICKS(50);   ///< 50 ms in ticks
    const uint8_t T100 = MS_TO_TICKS(100); ///< 100 ms in ticks
    const uint8_t T250 = MS_TO_TICKS(250); ///< 250 ms in ticks

    // --- persistent state ---
    static uint16_t counter = 0; ///< counts ticks for current state
    static uint8_t state = 0;    ///< current step in the sequence
    static uint8_t cycle = 0;    ///< cycle counter (0–2)

    if (!bLedEnabled)
        return;

    counter++;

    switch (state)
    {
    case 0: // all LEDs off, wait 250 ms
        leds_off();
        if (counter >= T250)
        {
            counter = 0;
            state = 2;
        }
        break;

    case 2: // LED 1–2 + 7–8 on, wait 50 ms
        VPORTA.OUT |= (PA1_SET_MASK | PA3_SET_MASK);
        if (counter >= T50)
        {
            counter = 0;
            state = 5;
        }
        break;

    case 5: // all LEDs off, wait 100 ms
        leds_off();
        if (counter >= T100)
        {
            counter = 0;
            state = 7;
        }
        break;

    case 7: // LED 1–2 + 7–8 on, wait 50 ms
        VPORTA.OUT |= (PA1_SET_MASK | PA3_SET_MASK);
        if (counter >= T50)
        {
            counter = 0;
            state = 10;
        }
        break;

    case 10: // all LEDs off, wait 250 ms
        leds_off();
        if (counter >= T250)
        {
            counter = 0;
            state = 12;
        }
        break;

    case 12: // LED 3–6 on, wait 50 ms
        VPORTA.OUT |= PA2_SET_MASK;
        if (counter >= T50)
        {
            counter = 0;
            state = 14;
        }
        break;

    case 14: // all LEDs off, wait 100 ms
        leds_off();
        if (counter >= T100)
        {
            counter = 0;
            state = 16;
        }
        break;

    case 16: // LED 3–6 on, wait 50 ms
        VPORTA.OUT |= PA2_SET_MASK;
        if (counter >= T50)
        {
            counter = 0;
            state = 18;
        }
        break;

    case 18: // all LEDs off, wait 250 ms
        leds_off();
        if (counter >= T250)
        {
            counter = 0;
            if (++cycle >= 3)
            {
                cycle = 0;
                state = 20; // special all-LEDs-on state
            }
            else
            {
                state = 0; // restart normal cycle
            }
        }
        break;

    case 20: // special: all LEDs on for 250 ms
        VPORTA.OUT |= (PA1_SET_MASK | PA2_SET_MASK | PA3_SET_MASK);
        if (counter >= T250)
        {
            counter = 0;
            state = 0; // restart normal sequence
        }
        break;
    }
}