Notes to help with building/setting up GCC toolchain for the AVR target, and specifically making it work with the new tinyAVR 1-series microcontrollers.

Attiny1614 is used as an example. It is a tinyAVR 1-series MCU, classified in GCC under avrxmega3 architecture.

Recent GCC versions support it as a target, but current avr-libc (2.0.0) does not (yet?), which requires the workaround described here.

With obivous modifications (in AVR-Libc section), this should probably work with other tinyAVR 1-series, like:

• attiny212, attiny214,
• attiny412, attiny414, attiny416, attiny417,
• attiny814, attiny816, attiny817,
• attiny1614, attiny1616, attiny1617,
• attiny3214, attiny3216, attiny3217.

Summary:

• Compilation/build toolchain:
  • Binutils
  • GCC: recent upstream GCC already supports the new MCUs (and avrxmega3 architecture)
  • AVR-Libc: upstream version (as of 2.0.0) does not have support for avrxmega3, so we need to hack things a bit:
    • We need 2 extra avrxmega3-specific files: libm.a and libc.a,
    • Also 3 extra MCU-specific files, e.g. for attiny1614: libattiny1614.a, crtattiny1614.o, iotn1614.h.
• Uploading firmare:
  • avrdude with a modified config file containing descriptions of the new AVR parts and jtag2updi protocol.
  • Setup another AVR (e.g. an Arduino Uno board) as the programmer using firmware by El Tangas implementing jtag2updi.

AVR GCC cross compilation + avrdude toolchain

Start by chosing the installation destination.

Used only during build/install:

export PREFIX=/usr/local/avr  # or some other dir

Needed for build/install and to invoke avr-gcc (obviously):

export PATH=$PATH:$PREFIX/bin

Binutils:

Download (www.gnu.org/software/binutils/), unpack and enter into directory, then:

mkdir avr-obj
cd avr-obj
../configure --prefix=$PREFIX --target=avr --disable-nls

make
sudo make install

Note: here an onwards, sudo is only needed because of /usr/local/... destination (the $PREFIX variable). If it's user-writable, don't use sudo.

GCC:

Download (www.gnu.org/software/gcc/), unpack and enter into directory, then:

# You may need to manually download GCC's prerequisites:
# (run this from top-level gcc build directory)
./contrib/download_prerequisites

# Continue to build:
mkdir avr-obj
cd avr-obj
../configure --prefix=$PREFIX --target=avr --enable-languages=c,c++ \
    --disable-nls --disable-libssp --with-dwarf2

make
sudo make install

AVR-Libc:

Download (http://download.savannah.gnu.org/releases/avr-libc/), unpack and enter into directory, then:

./configure --prefix=$PREFIX --build=`./config.guess` --host=avr
make
sudo env "PATH=$PATH" make install

Notice the extra 'env' -- install script needs to run avr-ranlib, which is found only under the new custom $PATH, which is (by default) not passed by sudo.

At this point you should be able to use avr-gcc toolchain for older MCUs like attiny85, attiny841, atmega328p, etc. Next sections are for the newer tinyAVR 1-series.

Atmel/Microchip ATtiny_DFP Pack:

Microchip does not make it easy. Instead of them simply providing a full avr-libc to build, we have to hack things together. Hopefully "upstream" avr-libc will soon support tinyAVR 1-series (like attiny1614), and this could be skipped.

Get Atmel/Microchip ATtiny_DFP Pack (try http://packs.download.atmel.com/) It is called something like "Atmel.ATtiny_DFP.1.3.229.atpack". It's really just a zip archive with .atpack extention.

Unpack and enter into directory, then we must copy the following 3 files from Atmel pack:

• gcc/dev/attiny1614/avrxmega3/libattiny1614.a,
• gcc/dev/attiny1614/avrxmega3/crtattiny1614.o,
• include/avr/iotn1614.h:

sudo mkdir $PREFIX/avr/lib/avrxmega3
sudo cp gcc/dev/attiny1614/avrxmega3/libattiny1614.a $PREFIX/avr/lib/avrxmega3/
sudo cp gcc/dev/attiny1614/avrxmega3/crtattiny1614.o $PREFIX/avr/lib/avrxmega3/
sudo cp include/avr/iotn1614.h $PREFIX/avr/include/avr/

Note: Obviously, if you are using a part other than attiny1614, adjust file names accordingly.

You should see file structure similar to that of other (supported) MCUs, e.g. compare outputs of:

find $PREFIX -iname '*841*'   # support files for attiny841
find $PREFIX -iname '*1614*'  # support files for the new attiny1614

Atmel/Microchip libm/libc:

We also need avrxmega3-compatible libc.a and libm.a (avr-libc 2.0.0 does not have it).

Get Atmel/Microchip "avr8-gnu-toolchain-..." (e.g. http://distribute.atmel.no/tools/opensource/Atmel-AVR-GNU-Toolchain/3.6.1/avr8-gnu-toolchain-osx-3.6.1.495-darwin.any.x86_64.tar.gz or later), unpack and enter directory, then:

sudo cp avr/lib/avrxmega3/libm.a $PREFIX/avr/lib/avrxmega3/
sudo cp avr/lib/avrxmega3/libc.a $PREFIX/avr/lib/avrxmega3/

TODO

There are some differences in device-specs/specs-attiny1614 between "vanilla" GCC and Atmel/Microchip toolchains, specifically wrt

 --defsym=__RODATA_PM_OFFSET__=0x8000

being present in Atmel/Microchip's, but not "vanilla" GCC. Test if memory-mapped flash actually works.

Update: It appears there's no issue with GCC's device-spec. I confirmed the compiler can choose to put constant global objects into flash memory (without needing to specify PROGMEM, etc), and generated code can access it fine with ld instructions (instead of lpm). No special considerations needed, except making sure that -j .rodata is supplied to avr-objcopy command (which ensures the relevant section of the elf file is included in the final ihex firmware file).

Example of compiler usage:

Compile and link:

avr-gcc -c -Os -mmcu=attiny1614 main.cpp
avr-gcc -mmcu=attiny1641 -o main.elf main.o

If you want to check section sizes:

avr-size main.elf

If you want to check disassembled output:

avr-objdump -S main.elf > main.asm

Create ihex file for uploading (e.g. with avrdude):

avr-objcopy -j .text -j .data -j .rodata -O ihex main.elf main.hex

avrdude

Note: avrdude build/installation requires presence of yacc and lex binaries, but the configure script doesn't seem to correctly check for that. In case of Ubuntu, you can get these from following packages:

sudo apt-get install bison flex

Download avrdude (http://download.savannah.gnu.org/releases/avrdude/), unpack and enter into directory, then:

mkdir avr-obj
cd avr-obj
../configure --prefix=$PREFIX

make
sudo make install

Using UPDI with jtag2updi:

The new AVRs (tinyAVR 0-series, tinyAVR 1-series, megaAVR 0-series) use a new protocol of uploading firmware - UPDI.

Some official programmer from Atmel/Microchip with UPDI support should work fine, but we can also have a setup where we use another AVR as the programmer, i.e. similar to how "Arduino as ISP" is commonly used for programming (old) attiny parts.

Thanks to the work of El Tangas and others, we have such firmware which, if uploaded to atmega328p (or similar) based board (e.g. Arduino Uno, Arduino Pro Mini, or even bare atmega328p, etc), will make it act as a UPDI programmer.

More details and wiring diagram: https://github.com/ElTangas/jtag2updi. In my case just uploading the pre-built build/JTAG2UPDI.hex to an Arduino Pro Mini was sufficient.

As of version 6.3 upstream avrdude does not yet support UPDI, but (again thanks to the work of El Tangas and others), all we need is a modified avrdude.conf file: https://github.com/ElTangas/jtag2updi/blob/master/avrdude.conf -- it adds the necessary entries for the new AVR parts and jtag2updi programmer protocol description to comminucate with your "Arduino as UPDI-programmer".

You do not need to override you "official" avrdude.conf file, since you can always specify a custom .conf path with -c flag (see example below).

Example of uploading firmware:

Assuming you've produced main.hex as described above, you can use avrdude with following script:

#!/bin/bash

# Adjust these as needed:
AVRDUDE_CONF_WITH_JTAG2UPDI=avrdude.conf
MCU=t1614
PORT=/dev/ttyUSB0

avrdude -v -C $AVRDUDE_CONF_WITH_JTAG2UPDI -c jtag2updi \
    -P $PORT -p $MCU \
    -U flash:w:main.hex:i