Improve hardcoded bootloader code

Author: m3y54m

.clang-format

@@ -0,0 +1,20 @@
+# This .clang-format file is tailored for C projects following widely accepted best practices.
+# It enforces readability, consistency, and compatibility with most open source C codebases.
+BasedOnStyle: LLVM
+Language: C
+IndentWidth: 4
+TabWidth: 4
+UseTab: Never
+ColumnLimit: 80
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLoopsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: InlineOnly
+BreakBeforeBraces: Allman
+SpaceBeforeParens: ControlStatements
+PointerAlignment: Left
+SortIncludes: true
+IncludeBlocks: Preserve
+IndentCaseLabels: true
+AlignConsecutiveAssignments: true
+AlignConsecutiveDeclarations: true
+AlignTrailingComments: true

.github/workflows/build.yml

@@ -43,5 +43,5 @@ jobs:
       with:
         name: bootloader
         path: |
-          build/bootloader/bootloader.bin
-          build/bootloader/bootloader.hex
+          build/bootloader_hardcoded/bootloader_hardcoded.bin
+          build/bootloader_hardcoded/bootloader_hardcoded.hex

CMakeLists.txt

@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
+
 # Use the AVR toolchain file (set before project())
 set(CMAKE_TOOLCHAIN_FILE ${CMAKE_CURRENT_SOURCE_DIR}/toolchain.cmake CACHE STRING "AVR toolchain file")
 project("AVR Bootloader" C)
@@ -9,6 +10,7 @@ project("AVR Bootloader" C)
 
 # MCU and clock settings
 set(MCU atmega328p)
+
 # This definition is essential for libraries like <util/delay.h>
 set(F_CPU 16000000UL)
 
@@ -25,17 +27,18 @@ set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Os -mmcu=${MCU} -DF_CPU=${F_CPU}")
 
 # Add subprojects
 add_subdirectory(blinky)
-add_subdirectory(bootloader)
+add_subdirectory(bootloader_hardcoded)
 
 # Clean all build files and directories
-add_custom_target(clean_build
+add_custom_target(
+  clean_build
   COMMAND ${CMAKE_COMMAND} -E remove_directory "${CMAKE_BINARY_DIR}"
-  COMMENT "[[main]] Cleaning the entire build directory..."
+  COMMENT "[[${PROJECT_NAME}]] Cleaning the entire build directory..."
 )
 
 # Fully erase the flash and EEPROM (if present) of the microcontroller
 add_custom_target(
   erase_flash
   COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -e
-  COMMENT "[[main]] Erasing the flash and EEPROM of \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+  COMMENT "[[${PROJECT_NAME}]] Erasing the flash and EEPROM of \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
 )

README.md

@@ -44,7 +44,6 @@ int main(void)
   while (1)
   {
     PORTB ^= (1 << PB5); // Toggle the LED
-
     _delay_ms(100); // Wait for 100 ms
   }
 
@@ -306,23 +305,23 @@ Data:        162 bytes (7.9% Full)
 
 This means that the total size of the `bootloader` program is 664 bytes. As you may noted that 162 bytes is exactly the size of `blinky` program stored in an array inside the `bootloader` program.
 
-By setting the boot section size of flash memory to 512 words (1024 bytes) we can fit our bootloader program (664 bytes) in it. With this configuration the start address of the boot section becomes `0x3E00` (in words). By knowing that each word is equal to 2 bytes, the start address becomes `0x3E00 * 2 = 0x7C00`.
+By setting the boot section size of flash memory to 1024 words (2048 bytes) we can fit our bootloader program (664 bytes) in it. With this configuration the start address of the boot section becomes `0x3C00` (in words). By knowing that each word is equal to 2 bytes, the start address becomes `0x3C00 * 2 = 0x7800`.
 
 ![image](https://github.com/m3y54m/simple-avr-bootloader/assets/1549028/974ef4eb-b016-4100-91b5-719db5d217f1)
 
 ![image](https://github.com/m3y54m/simple-avr-bootloader/assets/1549028/43a6f9f8-abd5-4ee9-9da1-82fe69b287c5)
 
 ```
-avrdude -c usbasp -p m328p -U lfuse:w:0xFF:m -U hfuse:w:0xDC:m -U efuse:w:0xFD:m
+avrdude -c usbasp -p m328p -U lfuse:w:0xFF:m -U hfuse:w:0xDA:m -U efuse:w:0xFD:m
 ```
 
-[Bootloader fuse bits setting in AVR® Fuse Calculator](https://www.engbedded.com/fusecalc/?P=ATmega328P&V_LOW=0xFF&V_HIGH=0xDC&V_EXTENDED=0xFD&O_HEX=Apply+values)
+[Bootloader fuse bits setting in AVR® Fuse Calculator](https://www.engbedded.com/fusecalc/?P=ATmega328P&V_LOW=0xFF&V_HIGH=0xDA&V_EXTENDED=0xFD&O_HEX=Apply+values)
 
-Adding `-Wl,-section-start=.text=0x7C00` flags to linker options of AVR-GCC makes start address of the bootloader program to be set on the start address of boot section.
+Adding `-Wl,-section-start=.text=0x7800` flags to linker options of AVR-GCC makes start address of the bootloader program to be set on the start address of boot section.
 
 ```
 avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -o build/main.o -c src/main.c
-avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -Wl,-section-start=.text=0x7C00 -o build/program.elf build/main.o
+avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -Wl,-section-start=.text=0x7800 -o build/program.elf build/main.o
 ```
 
 This is the contents of the output `.hex` file for the [`bootloader`](bootloader) program:

blinky/CMakeLists.txt

@@ -1,5 +1,8 @@
 cmake_minimum_required(VERSION 3.10)
-project(blinky C)
+
+# Dynamically set project name from directory name
+get_filename_component(PROJECT_NAME ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+project(${PROJECT_NAME} C)
 
 add_executable(${PROJECT_NAME}.elf src/main.c)
 

blinky/src/main.c

@@ -1,16 +1,18 @@
-
-// Blinky for AVR (ATmega328P)
-// Board connection:
-//   PB5 (Arduino Uno D13) ---> LED (with resistor)
-#define LED_PIN PB5
+/**
+ * @brief Blinky application for the ATmega328P.
+ * @details This application blinks an LED connected to pin PB5
+ * (Arduino Uno D13) at a 5Hz frequency.
+ */
 
 #include <stdint.h>
 #include <avr/io.h>
 #include <util/delay.h>
 
+#define LED_PIN PB5
+
 int main(void)
 {
-    // Set LED pin as output
+    // Configure LED pin as output
     DDRB |= (1U << LED_PIN);
 
     while (1)

bootloader/src/main.c

@@ -1,8 +1,25 @@
+
 cmake_minimum_required(VERSION 3.10)
-project(bootloader C)
+
+# Dynamically set project name from directory name
+get_filename_component(PROJECT_NAME ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+project(${PROJECT_NAME} C)
+
+# Set the start address for the bootloader (Boot Reset Vector) for ATmega328P
+# Fuse bits must be set accordingly to enable the bootloader section
+# BOOTSZ0 = 0, BOOTSZ1 = 1 for 1024 words (0x3C00 * 2 = 0x7800 for ATmega328P)
+set(BOOTLOADER_START_ADDRESS 0x7800)
+
+# Fuse bits for ATmega328P
+# Default values are set for a 16MHz external crystal with 1024 words bootloader size
+# CAUTION: Setting incorrect fuse bits can brick your microcontroller.
+# https://www.engbedded.com/fusecalc/
+set(LFUSE 0xFF)
+set(HFUSE 0xDA)
+set(EFUSE 0xFD)
 
 set(CMAKE_EXE_LINKER_FLAGS
-  "${CMAKE_EXE_LINKER_FLAGS} -Wl,-section-start=.text=0x7C00")
+  "${CMAKE_EXE_LINKER_FLAGS} -Wl,-section-start=.text=${BOOTLOADER_START_ADDRESS}")
 
 add_executable(${PROJECT_NAME}.elf src/main.c)
 
@@ -17,14 +34,6 @@ add_custom_target(
   COMMENT "[[${PROJECT_NAME}]] Building .hex and .bin files for \"${MCU}\""
 )
 
-# Fuse bits for ATmega328P
-# Default values are set for a 16MHz external crystal with 512 words bootloader size
-# CAUTION: Setting incorrect fuse bits can brick your microcontroller.
-# https://www.engbedded.com/fusecalc/
-set(LFUSE 0xFF CACHE STRING "Low fuse byte")
-set(HFUSE 0xDC CACHE STRING "High fuse byte")
-set(EFUSE 0xFD CACHE STRING "Extended fuse byte")
-
 # Write fuse bits
 add_custom_target(
   ${PROJECT_NAME}_write_fusebits
@@ -39,4 +48,5 @@ add_custom_target(
   COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U flash:w:${PROJECT_NAME}.hex
   DEPENDS ${PROJECT_NAME}_build
   COMMENT "[[${PROJECT_NAME}]] Flashing the bootloader to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+  COMMENT "[[${PROJECT_NAME}]] Bootloader start address: 0x${BOOTLOADER_START_ADDRESS}"
 )