Merge pull request 'Disable CPU while Rear Light is not used' (#3) from feature/power-off into main

Reviewed-on: #3

README.md

@@ -76,7 +76,7 @@ Hardware: FT232 USB-UART adapter connected to UPDI with a 4.7 kΩ resistor.
    ```
 4. Flash using pymcuprog:
    ```bash
-    pymcuprog -t uart -u /dev/ttyUSB0 -d attiny202 write -f build/main.hex
+    pymcuprog -t uart -u /dev/ttyUSB0 -d attiny202 erase && pymcuprog -t uart -u /dev/ttyUSB0 -d attiny202 write -f build/main.hex
    ```
 ## Hardware Setup (FT232 → ATtiny202 UPDI)
    ```bash

main.c

@@ -8,8 +8,10 @@
 #include <stdbool.h>
 #include <avr/io.h>
 #include <util/delay.h>
+#include <avr/sleep.h>
+#include <avr/interrupt.h>
 
-#define BUTTON_PIN_MASK 0x01 // PA0 TODO: using RESET/UPDI pin
+#define BUTTON_PIN_MASK 0x01 // PA0 used as RESET/UPDI pin
 #define PA1_SET_MASK 0x02    ///< LED 1–2
 #define PA2_SET_MASK 0x04    ///< LED 3–6
 #define PA3_SET_MASK 0x08    ///< LED 7–8
@@ -18,7 +20,9 @@
 
 #define MAIN_LOOP_SLEEP 10U                 // Main loop delay in ms
 #define BUTTON_LONG_PRESS_DURATION_MS 1000U // Long press threshold
-#define BUTTON_IGNORE_DURATION_MS 1000U     // Time button ignored after long press
+#define BUTTON_IGNORE_DURATION_MS 2000U     // Time button ignored after long press
+#define BUTTON_CONFIRMATION_BLINK_LOOPS 10U // Blink animation for confirmation
+#define BUTTON_CONFIRMATION_BLINK_DURATION_MS 50U
 
 /** Convert milliseconds to system ticks */
 #define MS_TO_TICKS(ms) ((ms) / MAIN_LOOP_SLEEP)
@@ -33,6 +37,8 @@ static inline void leds_off(void);
 static inline void leds_on(void);
 static void battery_level_indicator(void);
 static void handleSwitch(void);
+static void software_reset(void);
+ISR(PORTA_PORT_vect);
 
 /**
  * @brief Main entry point
@@ -66,19 +72,32 @@ int main(void)
             leds_off();
         }
 
-        // Long press detected → show confirmation blink
+        // Long press detected --> show confirmation blink
         if (bLedEnabledOld != bLedEnabled)
         {
             bLedEnabledOld = bLedEnabled;
 
-            leds_off();
-            _delay_ms(BUTTON_IGNORE_DURATION_MS / 10);
-            leds_on();
-            _delay_ms(BUTTON_IGNORE_DURATION_MS / 10);
-            leds_off();
+            for (uint8_t i = 0U; i < BUTTON_CONFIRMATION_BLINK_LOOPS; i++)
+            {
+                leds_off();
+                _delay_ms(BUTTON_CONFIRMATION_BLINK_DURATION_MS);
+                leds_on();
+                _delay_ms(BUTTON_CONFIRMATION_BLINK_DURATION_MS);
+                leds_off();
+            }
+
+            // Give time until button is released
             _delay_ms(BUTTON_IGNORE_DURATION_MS);
 
-            blinkLed(true); // reset blink state machine
+            // Activate the interrupt for PA0
+            PORTA.PIN0CTRL = PORT_PULLUPEN_bm | PORT_ISC_FALLING_gc;
+
+            set_sleep_mode(SLEEP_MODE_STANDBY); // Deepest sleep mode (standby)
+            sleep_enable();                     // Enable sleep
+
+            cli();       // Disable global interrupts
+            sei();       // Re-enable interrupts
+            sleep_cpu(); // MCU sleeps here
         }
         else
         {
@@ -149,6 +168,32 @@ static void handleSwitch(void)
     prevPressed = pressed;
 }
 
+/**
+ * @brief Perform software reset
+ */
+static void software_reset(void)
+{
+    CCP = CCP_IOREG_gc; // unlock protected registers
+    RSTCTRL.SWRR = 1;   // trigger software reset
+    while (1)
+        ; // wait for reset
+}
+
+/**
+ * @brief Interrupt service routine
+ */
+ISR(PORTA_PORT_vect)
+{
+    // Clear interrupt flags for PA0
+    PORTA.INTFLAGS = BUTTON_PIN_MASK;
+
+    if (!(VPORTA.IN & BUTTON_PIN_MASK)) // check PA0 low
+    {
+        // Turn off all LEDs
+        software_reset();
+    }
+}
+
 /**
  * @brief LED blink state machine (bike rear light style)
  *