// 2023-01-05, DMW, basic blink sketch plus lots of help from online resources

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  // pinMode(LED_BUILTIN, OUTPUT);

  asm volatile (
    // "sbi %0, %1 \n" //pinMode(13, OUTPUT);
    // sbi - Sets a specified bit in an I/O Register
    "sbi %[reg], %[reg_bit] \n" //pinMode(13, OUTPUT);
    : /* no return values */
    : [reg] "I" (_SFR_IO_ADDR(DDRB)), [reg_bit] "I" (DDB5) /* input values */
    : /* no registers clobbered */
  );
}

// digitalWrite(LED_BUILTIN, HIGH);  // turn the LED on (HIGH is the voltage level)
void led_on() {
  asm volatile(
    "sbi %[reg], %[reg_bit]   \n" // turn LED ON
    : /* no return values */
    : /* input values */
     [reg] "I" (_SFR_IO_ADDR(PORTB)), [reg_bit] "I" (PORTB5) 
    /* [reg] <-- named parameter, this is the register we want to change
       "I" <-- 6-bit data-type
       (_SFR_IO_ADDR(PORTB)) <-- C macro expression for providing the address for PORTB
       [reg_bit] <-- bit to set, named parameter, "I" <-- 6 bit value
       (PORTB5) <-- port B fifth bit, which is pin 13
    */  
    : /* no registers clobbered */
  );
}
// a lot of useful information about inline assembly and the strange 
// syntax and parameters in inline asm()
// https://www.nongnu.org/avr-libc/user-manual/inline_asm.html


// digitalWrite(LED_BUILTIN, LOW);   // turn the LED off by making the voltage LOW
void led_off() {
  asm volatile(
    "cbi %[reg], %[reg_bit]   \n" // turn LED OFF
    : /* no return values */
    : [reg] "I" (_SFR_IO_ADDR(PORTB)), [reg_bit] "I" (PORTB5) /* input values */
    : /* no registers clobbered */
  );
}

// the loop function runs over and over again forever
void loop() {
  // digitalWrite(LED_BUILTIN, HIGH);  // turn the LED on (HIGH is the voltage level)
  led_on();
  delay(1000);                      // wait for a second
  // digitalWrite(LED_BUILTIN, LOW);   // turn the LED off by making the voltage LOW
  led_off();
  delay(1000);                      // wait for a second
}