Developing for the Atmel AVR Microcontroller on Linux

Program space is a contiguous block of Flash memory, 16-bits wide that can be erased/rewritten 10,000 times. You can design your circuit to allow firmware upgrades in-circuit, using in-system programming.

All AVRs have some EEPROM, and most have SRAM; both are 8-bits wide. The EEPROM is designed to withstand at least 100,000 erase/write cycles. EEPROM is useful because it can be written from within your embedded program to retain data, even without a power supply, or during programming, such as for production-line calibration.

All AVRs, from the tiny 8-pin DIPs to the 44-pin Megas, have at least one data port. Data ports allow for input or output of logic-level data. The AVR ports are bidirectional, allowing you to set them for input or output on a pin-by-pin basis.

Many of the AVRs include additional hardware peripherals, such as UARTs for serial communication and calibrated RC oscillators used as internal system clocks. The external pins often serve two or more purposes, and how they are used depends on how you've configured the microcontroller. For instance, Figure 1 shows that certain I/O lines from both ports can be used with the multiplexed A/D converter.

The set of tools described here isn't the only one available, but it allows you to do basically anything, and the tools function well together. The toolkit is comprised of Binutils, GCC, AVR Libc and our Makefile template to write and build programs for the AVR microcontrollers; GDB and simulavr to debug your software; and avrdude as well as a hardware programmer to transfer your software to the microcontrollers. See the on-line Resources for download URLs for all software.

Fortunately, the recent versions of all these tools include support for the AVR platform, so installation is straightforward. We assume you've chosen to install everything under /usr/local/AVR.

Download a fresh copy of the current binutils source by following the link in the Resources. Untar the source, move into the binutils-X.XX directory and run:

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

The /usr/local/AVR/bin directory now contains AVR versions of ld, as, ar and the other binutils executables. Add the /usr/local/AVR/bin directory to your PATH now. You can apply the modification system-wide by adding:

PATH="$PATH:/usr/local/AVR/bin"

to the /etc/profile file. Make sure the directory is in your PATH and that the change has taken effect before proceeding.

After retrieving a recent release of the Gnu Compiler Collection from a mirror, run the following commands from within the unpacked top-level source directory:

$ ./configure --prefix=/usr/local/AVR \
        --target=avr --enable-languages="c,c++" \
        --disable-nls
$ make
# make install

This builds C and C++ compilers for AVR targets and installs avr-gcc and avr-g++ in /usr/local/AVR/bin.

The AVR Libc package provides a subset of the standard C library for AVR microcontrollers, including math, I/O and string processing utilities. It also takes care of basic AVR startup procedures, such as initializing the interrupt vector table, stack pointer and so forth. To install, get the latest release of the library and run the following from the top-level source directory:

$ unset CC
$ PREFIX=/usr/local/AVR ./doconf
$ ./domake
# ./domake install

The Psychogenic team has created a standard Makefile template that simplifies AVR project management. You can customize it easily for all your assembly, C and C++ AVR projects. It provides everything for a host of make targets, from compilation and upload to the microcontroller to debugging aids, such as source code intermixed with disassembly, and helpful gdbinit files. A detailed discussion of the template is available, and the Makefile template is available as Listing 1 on the Linux Journal FTP site (see Resources). Store the template with the other AVR tools, moving it to /usr/local/AVR/Makefile.tpl.