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--- en:multiasm:piot:chapter_4_9 [2024/09/27 23:22] – created pczekalski
+++ en:multiasm:piot:chapter_4_9 [2026/01/20 12:59] (current) – [Examples] ktokarz
@@ Line 1: / Line 1: @@
-======3 levels of programming: C++, libraries, assembler======
+====== 3 Levels of Programming: C++, Libraries, Assembler ======
+Programming AVR microcontrollers can be divided into three levels: C++, libraries, and assembler. Each of these levels offers distinct benefits and is utilized according to the project's specific requirements.
+  * **C++** is a high-level language that allows programmers to write code in a more abstract and understandable way. Using C++ for AVR enables advanced features such as object-oriented programming, inheritance, and polymorphism. This makes the code more modular and easier to maintain. Compilers like AVR-GCC convert C++ code into machine code that the microcontroller can execute.
+  * **Libraries** are sets of predefined functions and procedures that facilitate programming AVR microcontrollers. An example is the AVR Libc library, which provides functions for I/O, memory management, and mathematical operations. Using libraries enables rapid application development without writing code from scratch. Libraries are particularly useful in projects that require frequent use of standard functions.
+  * **Assembler** is a low-level language that allows direct programming of the AVR microcontroller. Writing code in assembler gives full control over the hardware and allows for performance optimization. However, programming in assembler requires a deep understanding of the microcontroller's architecture and is more complex than programming in C++. An assembler is often used in critical applications where every clock cycle counts.
+The choice of programming level depends on the project's specifics. C++ is ideal for creating complex applications, libraries facilitate rapid prototyping, and assembler provides maximum control and performance. Each of these levels has its place in AVR microcontroller programming.''
+Some AVR assembly examples for the Arduino Uno (ATmega328P), ready to drop directly into the Arduino IDE using inline assembly - asm volatile().
+===== Examples =====
+**Blink inbuilt LED on pin 13 (port PB5) using assembly**
+<code c>
+  void setup() {
+    // Set PB5 (pin 13) as output  // if DDRB (Data Direction Register B) = 1, PORTB is output
+    asm volatile("sbi 0x04, 5");   // DDRB |= (1<<5)
+  }
+  void loop() {
+    asm volatile("sbi 0x05, 5");   // LED ON  (PORTB |= (1<<5))
+    delay(500);
+    asm volatile("cbi 0x05, 5");   // LED OFF (PORTB &= ~(1<<5))
+    delay(500);
+  }
+</code>
+For Arduino Uno (ATmega328P):
+  * DDRB has address 0x04
+  * PORTB has address 0x05
+----
+**Add two numbers using AVR registers**
+<code c>
+  void setup() {
+    Serial.begin(9600);
+    uint8_t a = 7, b = 9, result;
+    asm volatile(
+      "mov r24, %1\n"   // r24 = a
+      "mov r25, %2\n"   // r25 = b
+      "add r24, r25\n"  // r24 = a + b
+      "mov %0, r24\n"   // result = r24
+      : "=r"(result)    // agrument %0
+      : "r"(a), "r"(b)  // arguments %1, %2
+      : "r24", "r25", "cc" // preserve the content of r24 and r25
+    );
+    Serial.println(result);
+  }
+  void loop() {}
+</code>
+----
+**Read digital input (PD2, bit 2 on PORTD)**
+<code c>
+  void setup() {
+    Serial.begin(9600);
+    asm volatile("cbi 0x0A, 2");   // DDRD &= ~(1<<2) → PD2 as input
+  }
+  void loop() {
+    uint8_t value;
+    asm volatile(
+      "in %0, 0x09"     // Read PIND
+      : "=r"(value)
+    );
+    Serial.println(value & (1<<2));
+    delay(200);
+  }
+</code>