AVR: Alf and Regards's RISC Processor

Installing AVR toolchain:

Basic requirements:

gcc-avr : a GNU C cross-compiler for specifically for AVR

avr-libc: it is a package for AVR C library
more info:  https://www.nongnu.org/avr-libc/user-manual/index.html
			https://exploreembedded.com/wiki/AVR_C_Library


avrdude: it is a utility that transfers codes from the UBUNTU to the microcontroller. AVR downloader uploader: software(utility program)  for downloading and uploading on-chip memories of Microchip's AVR microcontrollers

arduino CLI: Arduino Command LIne Interface- Arduino CLI is a command line tool that contains all you need to easily build applications around the Arduino ecosystem.


Basic installation commands:
sudo apt-get install gcc-avr binutils-avr avr-libc
sudo apt-get install avrdude
sudo apt-get install arduino-cli or snap install arduino-cli

More info about installation: https://www.nongnu.org/avr-libc/user-manual/install_tools.html



Basic processes involved:
1)Compilation which creates object files
2)Linking the object files to create ELF files(Executable and Linkable Format)
3)Object-copy(assembly) to create hex files
4)Flashing(dumping) the hex file on the board using avrdude


more info: https://www.avrfreaks.net/forum/avr-gcc-compiling-linking-and-assembly --(pic in this website)--


Instructions to compile the code:
Compile and linking Instruction(generating object files and linking them):
avr-gcc -Os -mmcu=atmega2560 -c -o <destination_file-blinking_led> <source.c> //avoid using '-c' to avoid improper linking 

Object Copy Instruction:
avr-objcopy -O ihex -R .eeprom <destination_file-blinking_led>  <file_name.hex>

Programming(flashing the hex file on board):
avrdude -C /usr/share/arduino/hardware/tools/avrdude.conf -patmega2560 -cwiring  -P /dev/ttyACM0 -b 115200 -D -U flash:w:<file_name.hex>:i 



Execution using make:

GNU make:
The "make" utility automates the mundane aspects of building executable from source code. "make" uses a so-called makefile, which contains rules on how to build the executables. Make is different from a script as a script shows no intelligence. All instructions run blindly, without dpending on the consequences of the previous instructions.

more info: https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html#zz-1.6
makefile youtube tutorial: https://www.youtube.com/playlist?list=PLNmACol6lYY7Dzvg7jKgvMdDaDEDFnNqD

based on the makefile created..
//change parameters accordingly in makefile to make sure the correct files get executed
Instructions:
make all
make flash

Makefile:
# simple AVR Makefile
#
# written by michael cousins (http://github.com/mcous)
# released to the public domain

# Makefile
#
# targets:
#   all:    compiles the source code
#   test:   tests the isp connection to the mcu
#   flash:  writes compiled hex file to the mcu's flash memory
#   fuse:   writes the fuse bytes to the MCU
#   disasm: disassembles the code for debugging
#   clean:  removes all .hex, .elf, and .o files in the source code and library directories

# parameters (change this stuff accordingly)
# project name
PRJ = main
# avr mcu
MCU = atmega2560
# mcu clock frequency
CLK = 16000000
# avr programmer (and port if necessary)
# e.g. PRG = usbtiny -or- PRG = arduino -P /dev/tty.usbmodem411
PRG = wiring -P /dev/ttyACM0
# fuse values for avr: low, high, and extended
# these values are from an Arduino Uno (ATMega328P)
# see http://www.engbedded.com/fusecalc/ for other MCUs and options
LFU = 0xFF
HFU = 0xD0
EFU = 0xFD
# program source files (not including external libraries)
SRC = $(PRJ).c
# where to look for external libraries (consisting of .c/.cpp files and .h files)
# e.g. EXT = ../../EyeToSee ../../YouSART
EXT =


#################################################################################################
# \/ stuff nobody needs to worry about until such time that worrying about it is appropriate \/ #
#################################################################################################

# include path
INCLUDE := $(foreach dir, $(EXT), -I$(dir))
# c flags
CFLAGS    = -Wall -Os -DF_CPU=$(CLK) -mmcu=$(MCU) $(INCLUDE)
# any aditional flags for c++
CPPFLAGS =

# executables
AVRDUDE = avrdude  -C /usr/share/arduino/hardware/tools/avrdude.conf -c $(PRG) -p $(MCU)  -b 115200 -D
OBJCOPY = avr-objcopy
OBJDUMP = avr-objdump
SIZE    = avr-size --format=avr --mcu=$(MCU)
CC      = avr-gcc

# generate list of objects
CFILES    = $(filter %.c, $(SRC))
EXTC     := $(foreach dir, $(EXT), $(wildcard $(dir)/*.c))
CPPFILES  = $(filter %.cpp, $(SRC))
EXTCPP   := $(foreach dir, $(EXT), $(wildcard $(dir)/*.cpp))
OBJ       = $(CFILES:.c=.o) $(EXTC:.c=.o) $(CPPFILES:.cpp=.o) $(EXTCPP:.cpp=.o)

# user targets
# compile all files
all: $(PRJ).hex

# test programmer connectivity
test:
	$(AVRDUDE) -v

# flash program to mcu
flash: all
	$(AVRDUDE) -U flash:w:$(PRJ).hex:i

# write fuses to mcu
fuse:
	$(AVRDUDE) -U lfuse:w:$(LFU):m -U hfuse:w:$(HFU):m -U efuse:w:$(EFU):m

# generate disassembly files for debugging
disasm: $(PRJ).elf
	$(OBJDUMP) -d $(PRJ).elf

# remove compiled files
clean:
	rm -f *.hex *.elf *.o
	$(foreach dir, $(EXT), rm -f $(dir)/*.o;)

# other targets
# objects from c files
.c.o:
	$(CC) $(CFLAGS) -c $< -o $@

# objects from c++ files
.cpp.o:
	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@

# elf file
$(PRJ).elf: $(OBJ)
	$(CC) $(CFLAGS) -o $(PRJ).elf $(OBJ)

# hex file
$(PRJ).hex: $(PRJ).elf
	rm -f $(PRJ).hex
	$(OBJCOPY) -j .text -j .data -O ihex $(PRJ).elf $(PRJ).hex
	$(SIZE) $(PRJ).elf


main.c file for blinking of led code:
#include <avr/io.h>
#define F_CPU 16000000//16MHz
#define MS_DELAY 1000//1 second=1000 ms
#include <util/delay.h>

int main(void)
{
    //pin 37-port C0 
     DDRC = 0xff; 
    PORTC = 0xff;
    
    while(1)
    {
        PORTC = 0x01;
        _delay_ms(1000);//1 second delay
        PORTC = 0x00;
        _delay_ms(1000);//1 second delay
    }
    
    return 0;
}