Developing for the Atmel AVR Microcontroller on Linux

Using avr-gdb and simulavr in tandem, you can run your software on a choice of AVR microcontrollers through the simulator, while using GDB to step through and observe the executing code. Acquire the simulavr source from the project site and perform the installation:

$ ./configure --prefix=/usr/local/AVR \
  --with-avr-includes=/usr/local/AVR/avr/include
$ make # make install

Install GDB, built for AVR targets, by compiling the source as follows:

$ ./configure --target=avr \
     --prefix=/usr/local/AVR
$ make
# make install

When you finally have a program ready for testing on actual hardware, you need some way to upload the data and write it to the microcontroller's Flash program memory. AVRDUDE and a compatible hardware programmer are the last components of the development kit. Grab a copy of the AVRDUDE source and install it with:

$ ./configure --prefix=/usr/local/AVR
$ make
# make install

You now have installed every software component required for a complete AVR development environment. All you need is the physical means to transfer programs to microcontrollers.

AVRDUDE supports a number of different hardware programmer configurations. The simplest systems are described on the AVRDUDE site and are comprised of little more than a parallel port connector, a ceramic oscillator and a DIP socket. These are powered directly off the computer's port and may not work for everyone.

Figure 2. Home-Brew PPI Programmer PCB

A step up in complexity, independently powered, buffered in-system programmers can be built easily (see Resources). Two programmers requiring only a few parts are discussed on the Psychogenic Web page, which describes the schematics, provides artwork and has complete instructions on creating your own printed circuit boards (as depicted in Figure 2) for the programmers.

Figure 3. Atmel STK500 Development Kit

A number of commercial solutions also are available. If you're interested in easily programming a wide selection of the AVR family, go with Atmel's STK500 kit. More than a simple programmer, the STK500 is a starter kit that allows you to program the microcontrollers and easily prototype new designs. It includes a number of LEDs and switches, an oscillator, RS-232 interface and other niceties that easily can be interfaced with your target chip.

Our focus here is on the development system rather than on programming for the AVR platform. The AVR Libc documentation is a good place to start for information on programming AVRs in Assembly, C and C++.

The Hello World program of the microcontroller universe is the classic flashing LEDs. A slightly different take on this theme, which Knight Rider fans should appreciate, is available on the Linux Journal FTP site, where you can download C (Listing 2) or C++ (Listing 3) versions of an example program that cycles each of eight light-emitting diodes (LEDs) back and forth.

Create a project directory—for instance, ~/helloavr/—and retrieve the program, saving Listing 2 as ~/helloavr/kr.c and Listing 3 as ~/helloavr/kitt.cpp. Also, copy the Makefile template, /usr/local/AVR/Makefile.tpl, to ~/helloavr/Makefile.

Using this Makefile is easy and makes compilation a snap. Open the Makefile in your favourite editor and modify the configuration section, near the top of the file, so that the MCU, PROJECTNAME and PRJSRC variables are set as shown in Listing 4. The MCU variable determines the AVR family member for which we are compiling the program, and the PRJSRC variable lists all the Assembly, C and C++ source files used in the project.

#####         Target Specific Details          #####
#####     Customize these for your project     #####

# Name of target controller
# (e.g. 'at90s8515', see the available avr-gcc mmcu
# options for possible values)
MCU=at90s8515

# Name of our project
# (use a single word, e.g. 'myproject')
PROJECTNAME=helloavr

# Source files
# List C/C++/Assembly source files:
# (list all files to compile, e.g. 'a.c b.cpp as.S')
# Use .cc, .cpp or .C suffix for C++ files, use .S
# (NOT .s !!!) for assembly source code files.
PRJSRC=kr.c

Once you've configured the Makefile, compiling and linking the program is as simple as typing make.

You can perform the compilation and linking steps manually instead, by issuing:

  $ avr-gcc -I.  -g -mmcu=at90s8515 -Os       \
             -fpack-struct -fshort-enums               \
             -funsigned-bitfields -funsigned-char \
             -Wall -Wstrict-prototypes -c kr.c

  $ avr-gcc -o helloavr.out kr.o

The most notable difference is the addition of the required -mmcu command-line argument, used to specify the target microcontroller. Either method compiles kr.c and creates the helloavr.out ELF-format program. This file cannot be executed on your development station but is used later during the debugging stage.

You also can build the C++ version of the program by doing a make clean, changing the Makefile PRJSRC variable to kitt.cpp and then issuing another make.