Implement SUP-based AVR bootloader and Python loader script

Author: m3y54m

.gitignore

@@ -6,4 +6,7 @@ build/
 
 # ...but do NOT ignore the cmake-kits.json file and the parent folder
 !.vscode/
-!/.vscode/cmake-kits.json
+!/.vscode/cmake-kits.json
+
+# Ignore Python cache files
+__pycache__/

CMakeLists.txt

@@ -18,7 +18,7 @@ set(MCU atmega328p)
 set(F_CPU 16000000UL)
 
 # UART Baud rate settings
-set(BAUD 9600)
+set(BAUD 57600)
 
 # Programmer for avrdude
 set(AVRDUDE_PROGRAMMER usbasp)
@@ -28,24 +28,47 @@ set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
 set(CMAKE_C_EXTENSIONS OFF)
 
+# Set the start address for the bootloader (Boot Reset Vector) for ATmega328P
+# Fuse bits must be set accordingly to enable the boot reset vector (BOOTRST = 0)
+# and set bootloader section size.
+# 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)
+
 # Common compiler flags for AVR targets
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Os -mmcu=${MCU} -DF_CPU=${F_CPU} -DBAUD=${BAUD}")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Os -mmcu=${MCU} -DF_CPU=${F_CPU} -DBAUD=${BAUD} -DMAX_USER_APP_SIZE=${BOOTLOADER_START_ADDRESS}")
 
 # Add subprojects
 add_subdirectory(blinky)
 add_subdirectory(bootloader_hardcoded)
 add_subdirectory(simple_uart_protocol)
+add_subdirectory(final)
 
 # Clean all build files and directories
 add_custom_target(
-  clean_build
+  all_clean_build
   COMMAND ${CMAKE_COMMAND} -E remove_directory "${CMAKE_BINARY_DIR}"
   COMMENT "[[${PROJECT_NAME}]] Cleaning the entire build directory..."
 )
 
 # Fully erase the flash and EEPROM (if present) of the microcontroller
 add_custom_target(
-  erase_flash
+  all_erase_flash
   COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -e
   COMMENT "[[${PROJECT_NAME}]] Erasing the flash and EEPROM of \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
-)
+)
+
+# Write fuse bits
+add_custom_target(
+  all_write_fusebits
+  COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U lfuse:w:${LFUSE}:m -U hfuse:w:${HFUSE}:m -U efuse:w:${EFUSE}:m
+  COMMENT "[[${PROJECT_NAME}]] Writing fuse bits to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+  COMMENT "[[${PROJECT_NAME}]] Fuse bits set to: L=${LFUSE}, H=${HFUSE}, E=${EFUSE}"
+)

README.md

@@ -59,7 +59,7 @@ int main(void)
 ```
 cd blinky
 mkdir build
-avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -o build/main.o -c src/main.c
+avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -o build/main.o -c main.c
 avr-gcc -Wall -Os -mmcu=atmega328p -std=c11  -o build/program.elf build/main.o
 ```
 
@@ -323,7 +323,7 @@ avrdude -c usbasp -p m328p -U lfuse:w:0xFF:m -U hfuse:w:0xDA:m -U efuse:w:0xFD:m
 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 -o build/main.o -c main.c
 avr-gcc -Wall -Os -mmcu=atmega328p -std=c11 -Wl,-section-start=.text=0x7800 -o build/program.elf build/main.o
 ```
 

blinky/CMakeLists.txt

@@ -4,7 +4,7 @@ cmake_minimum_required(VERSION 3.13)
 get_filename_component(PROJECT_NAME ${CMAKE_CURRENT_SOURCE_DIR} NAME)
 project(${PROJECT_NAME} C)
 
-add_executable(${PROJECT_NAME}.elf src/main.c)
+add_executable(${PROJECT_NAME}.elf main.c)
 
 add_custom_target(
   ${PROJECT_NAME}_build ALL

blinky/src/main.c renamed to blinky/main.c

@@ -5,23 +5,11 @@ cmake_minimum_required(VERSION 3.13)
 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)
-
+# Linker flags to set the bootloader start address
 set(CMAKE_EXE_LINKER_FLAGS
   "${CMAKE_EXE_LINKER_FLAGS} -Wl,-section-start=.text=${BOOTLOADER_START_ADDRESS}")
 
-add_executable(${PROJECT_NAME}.elf src/main.c)
+add_executable(${PROJECT_NAME}.elf main.c)
 
 # Build the hex and bin files
 # which are needed for flashing the bootloader
@@ -34,14 +22,6 @@ add_custom_target(
   COMMENT "[[${PROJECT_NAME}]] Building .hex and .bin files for \"${MCU}\""
 )
 
-# Write fuse bits
-add_custom_target(
-  ${PROJECT_NAME}_write_fusebits
-  COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U lfuse:w:${LFUSE}:m -U hfuse:w:${HFUSE}:m -U efuse:w:${EFUSE}:m
-  COMMENT "[[${PROJECT_NAME}]] Writing fuse bits to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
-  COMMENT "[[${PROJECT_NAME}]] Fuse bits set to: L=${LFUSE}, H=${HFUSE}, E=${EFUSE}"
-)
-
 # Flash the bootloader to the microcontroller
 add_custom_target(
   ${PROJECT_NAME}_flash

bootloader_hardcoded/CMakeLists.txt

@@ -172,7 +172,7 @@ static bool write_to_flash(const uint32_t destination_address, const uint8_t* so
             // Fill word into page buffer
             boot_page_fill(page_addr + offset, word_data);
         }
-
+        
         // Write page to flash
         boot_page_write(page_addr);
         // Wait for the write operation to complete
@@ -262,8 +262,8 @@ int main(void)
             // Loading failed - infinite error blink
             while (true)
             {
-               //led_blink(FAILURE_BLINKS_COUNT, FAILURE_BLINK_DELAY_MS);
-               //_delay_ms(2000);
+                led_blink(FAILURE_BLINKS_COUNT, FAILURE_BLINK_DELAY_MS);
+                _delay_ms(2000);
             }
         }
     }

bootloader_hardcoded/src/main.c renamed to bootloader_hardcoded/main.c

@@ -0,0 +1,88 @@
+
+cmake_minimum_required(VERSION 3.13)
+
+# Dynamically set project name from directory name
+get_filename_component(PROJECT_NAME ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+project(${PROJECT_NAME} C)
+
+add_executable(${PROJECT_NAME}_bootloader.elf bootloader/main.c ../simple_uart_protocol/sup.c)
+add_executable(${PROJECT_NAME}_user_app.elf user_app/main.c ../simple_uart_protocol/sup.c)
+
+# Use target_link_options to apply linker flags ONLY to the bootloader.
+# This is the correct, modern CMake way to handle this.
+target_link_options(${PROJECT_NAME}_bootloader.elf PRIVATE
+  "-Wl,-section-start=.text=${BOOTLOADER_START_ADDRESS}"
+)
+
+# Place a small dedicated section ".bootflag" at a fixed SRAM address so that
+# both bootloader and user application can reliably share a RAM-resident flag
+# across software resets without using EEPROM. Address chosen near top of SRAM
+# for ATmega328P; adjust if you use a different MCU.
+target_link_options(${PROJECT_NAME}_bootloader.elf PRIVATE
+  "-Wl,--section-start=.bootflag=0x08F8"
+)
+
+target_link_options(${PROJECT_NAME}_user_app.elf PRIVATE
+  "-Wl,--section-start=.bootflag=0x08F8"
+)
+
+# Generate a linker map file next to each ELF. Use the output file name derived from
+# the target name so the map is easy to find (e.g. final_bootloader.elf -> final_bootloader.map)
+target_link_options(${PROJECT_NAME}_bootloader.elf PRIVATE
+  "-Wl,-Map=${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}_bootloader.map"
+)
+
+target_link_options(${PROJECT_NAME}_user_app.elf PRIVATE
+  "-Wl,-Map=${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}_user_app.map"
+)
+
+# Build the hex and bin files
+# which are needed for flashing the bootloader
+add_custom_target(
+  ${PROJECT_NAME}_build_bootloader ALL
+  COMMAND avr-objcopy -j .text -j .data -O ihex ${PROJECT_NAME}_bootloader.elf ${PROJECT_NAME}_bootloader.hex
+  COMMAND avr-objcopy -j .text -j .data -O binary ${PROJECT_NAME}_bootloader.elf ${PROJECT_NAME}_bootloader.bin
+  COMMAND avr-size --format=avr --mcu=${MCU} ${PROJECT_NAME}_bootloader.elf
+  DEPENDS ${PROJECT_NAME}_bootloader.elf
+  COMMENT "[[${PROJECT_NAME}]] Building bootloader .hex and .bin files for \"${MCU}\""
+)
+
+add_custom_target(
+  ${PROJECT_NAME}_build_user_app ALL
+  COMMAND avr-objcopy -j .text -j .data -O ihex ${PROJECT_NAME}_user_app.elf ${PROJECT_NAME}_user_app.hex
+  COMMAND avr-objcopy -j .text -j .data -O binary ${PROJECT_NAME}_user_app.elf ${PROJECT_NAME}_user_app.bin
+  COMMAND avr-size --format=avr --mcu=${MCU} ${PROJECT_NAME}_user_app.elf
+  DEPENDS ${PROJECT_NAME}_user_app.elf
+  COMMENT "[[${PROJECT_NAME}]] Building user application .hex and .bin files for \"${MCU}\""
+)
+
+add_custom_target(
+  ${PROJECT_NAME}_build_all ALL
+  DEPENDS ${PROJECT_NAME}_build_bootloader ${PROJECT_NAME}_build_user_app
+  COMMENT "[[${PROJECT_NAME}]] Building all .hex and .bin files for \"${MCU}\""
+)
+
+# Flash the bootloader to the microcontroller
+add_custom_target(
+  ${PROJECT_NAME}_flash_bootloader
+  COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U flash:w:${PROJECT_NAME}_bootloader.hex:i
+  DEPENDS ${PROJECT_NAME}_build_bootloader
+  COMMENT "[[${PROJECT_NAME}]] Flashing the bootloader to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+  COMMENT "[[${PROJECT_NAME}]] Bootloader start address: 0x${BOOTLOADER_START_ADDRESS}"
+)
+
+# Flash the user application to the microcontroller
+add_custom_target(
+  ${PROJECT_NAME}_flash_user_app
+  COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U flash:w:${PROJECT_NAME}_user_app.hex:i
+  DEPENDS ${PROJECT_NAME}_build_user_app
+  COMMENT "[[${PROJECT_NAME}]] Flashing user application to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+)
+
+# Flash both the bootloader and user application to the microcontroller
+add_custom_target(
+  ${PROJECT_NAME}_flash_all
+  COMMAND avrdude -c ${AVRDUDE_PROGRAMMER} -p ${MCU} -U flash:w:${PROJECT_NAME}_user_app.hex:i -U flash:w:${PROJECT_NAME}_bootloader.hex:i
+  DEPENDS ${PROJECT_NAME}_build_all
+  COMMENT "[[${PROJECT_NAME}]] Flashing both bootloader and user application to \"${MCU}\" using \"${AVRDUDE_PROGRAMMER}\""
+)

final/CMakeLists.txt

@@ -0,0 +1,13 @@
+#ifndef BOOT_SYNC_H
+#define BOOT_SYNC_H
+
+#include <stdint.h>
+
+/**
+ * @brief A magic value to indicate a firmware update is requested.
+ */
+#define FW_UPDATE_INDICATOR_MAGIC 0xDEADBEEFU
+
+extern volatile uint32_t boot_sync_flag;
+
+#endif // BOOT_SYNC_H