--- /dev/null
+I've been wanting to get into microcontroller programming for a while
+now, and last week I broke down and ordered components for a
+[breadboard Arduino][breadboard-Arduino] from [Mouser]. There's a
+fair amount of buzz about the [Arduino][] platform, but I find the
+whole [sketch infrastucture][sketch] confusing. I'm a big fan of
+command line tools in general, so the whole IDE thing was a bit of a
+turn off.
+
+Because the [ATMega328][] doesn't have a USB controller, I also bought
+a [Teensy 2.0][Teensy] from [PJRC][]. The Teensy is just an
+[ATMega32u4][] on a board with supporting hardware (clock, reset
+switch, LED, etc). I've packed the Teensy programmer and HID listener
+in my [[Gentoo overlay]], to make it easier to install them and stay
+up to date.
+
+Arduinos (and a number of similar projects) are based on [AVR][]
+microcontrollers like the ATMegas. Writing code for an AVR processor
+is the similar to writing code for any other processor. [GCC][] will
+cross-compile your code once you've setup a cross-compiling toolchain.
+There's a good intro to the whole embedded approach in the [Gentoo
+Embedded Handbook][handbook].
+
+For all the AVR-specific features you can use [AVR-libc][], an open
+source C library for AVR processors. It's hard to imagine doing
+anything interesting without using this library, so you should at
+least skim through the manual. They also have a few interesting
+[demos][] to get you going.
+
+AVR-libc sorts chip-support code into AVR architecture subdirectories.
+For example, object code specific to my [ATMega32u4][] is installed at
+`/usr/avr/lib/avr5/crtm32u4.o`. `avr5` is the [AVR architecture
+version][arch] of this chip.
+
+Crossdev
+--------
+
+Since you will probably not want to build a version of GCC that runs
+on your AVR chip, you'll be building a cross comiling toolchain. The
+toolchain will allow you to use your development box to compile
+programs for your AVR chip. On Gentoo, the recommended approach is to
+use [crossdev][] to build the toolchain (although [crossdev's AVR
+support can be flaky][bug147155]). They suggest you install it in a
+[stage3 chroot to protect your native toolchain][chroot], but I think
+it's easier to just make [[btrfs]] snapshots of my hard drive before
+doing something crazy. I didn't have any trouble skipping the chroot
+on my sytem, but your mileage may vary.
+
+ # emerge -av crossdev
+
+Because it has per-arch libraries (like `avr5`), AVR-libc needs to be
+built with [multilib][] support. If you (like me) have avoided
+multilib like the plague so far, you'll need to patch crossdev to turn
+on multilib for the AVR tools. Do this by applying Jess'
+[patch][multilib-patch] from [bug 377039][bug377039].
+
+ # wget -O crossdev-avr-multilib.patch 'https://bugs.gentoo.org/attachment.cgi?id=304037'
+ # patch /usr/bin/crossdev < crossdev-avr-multilib.patch
+
+If you're using a profile where multilib is masked
+(e.g. `default/linux/x86/10.0/desktop`) you should use Niklas'
+[extended version of the patch][niklas-patch] from the duplicate [bug
+378387][bug378387].
+
+Despite claiming to use the last overlay in `PORTDIR_OVERLAY`,
+crossdev currently [uses the first][bug428420], so if you use
+[layman][] to manage your overlays (like [[mine|Gentoo_overlay]]),
+you'll want to tweak your `make.conf` to look like:
+
+ source /var/lib/layman/make.conf
+ PORTDIR_OVERLAY="/usr/local/portage ${PORTDIR_OVERLAY}"
+
+Now you can install your toolchain following the [Crossdev
+wiki][crossdev-avr]. First install a minimal GCC (stage 1) using
+
+ # USE="-cxx -openmp" crossdev --binutils 9999 -s1 --without-headers --target avr
+
+Then install a full featured GCC (stage 4) using
+
+ # USE="cxx -nocxx" crossdev --binutils 9999 -s4 --target avr
+
+I use `binutils-9999` to install live from the [git mirror][git],
+which avoids [a segfault bug in binutils 2.22][bug12161].
+
+After the install, I was getting bit by [bug 147155][bug147155]:
+
+ cannot open linker script file ldscripts/avr5.x
+
+Which I work around with:
+
+ # ln -s /usr/x86_64-pc-linux-gnu/avr/lib/ldscripts /usr/avr/lib/ldscripts
+
+Now you're ready. Go forth and build!
+
+Cross compiler construction
+---------------------------
+
+Why do several stages of GCC need to be built anyway? From `crossdev
+--help`, here are the stages:
+
+0. Build just binutils
+1. Also build a bare C compiler (no C library/C++/shared GCC libs/C++
+ exceptions/etc…)
+2. Also build kernel headers
+3. Also build the C library
+4. Also build a full compiler
+
+
+[breadboard-Arduino]: http://arduino.cc/en/Main/Standalone
+[Mouser]: http://www.mouser.com/
+[Arduino]: http://arduino.cc/
+[sketch]: http://arduino.cc/en/Guide/Environment
+[ATMega328]: http://www.atmel.com/devices/atmega328.aspx
+[Teensy]: http://pjrc.com/teensy/
+[PJRC]: http://pjrc.com/
+[ATMega32u4]: http://www.atmel.com/devices/atmega32u4.aspx
+[AVR]: http://en.wikipedia.org/wiki/Atmel_AVR
+[GCC]: http://gcc.gnu.org/
+[handbook]: http://www.gentoo.org/proj/en/base/embedded/handbook/
+[AVR-libc]: http://www.nongnu.org/avr-libc/
+[demos]: http://www.nongnu.org/avr-libc/user-manual/group__demos.html
+[arch]: http://www.nongnu.org/avr-libc/user-manual/using_tools.html#using_avr_gcc_mach_opt
+[crossdev]: http://en.gentoo-wiki.com/wiki/Crossdev
+[bug147155]: https://bugs.gentoo.org/show_bug.cgi?id=147155
+[chroot]: http://www.gentoo.org/proj/en/base/embedded/handbook/?part=1&chap=2#doc_chap1
+[multilib]: http://www.gentoo.org/doc/en/gentoo-amd64-faq.xml#multilib
+[multilib-patch]: https://bugs.gentoo.org/attachment.cgi?id=304037
+[bug377039]: https://bugs.gentoo.org/show_bug.cgi?id=377039
+[bug428420]: https://bugs.gentoo.org/show_bug.cgi?id=428420
+[layman]: http://layman.sourceforge.net/
+[crossdev-avr]: http://en.gentoo-wiki.com/wiki/Crossdev#AVR_Architecture
+[git]: http://sourceware.org/git/?p=binutils.git
+[niklas-patch]: https://bugs.gentoo.org/attachment.cgi?id=285901
+[bug378387]: https://bugs.gentoo.org/show_bug.cgi?id=378387
+[bug12161]: http://sourceware.org/bugzilla/show_bug.cgi?id=12161
+[link]: http://en.gentoo-wiki.com/wiki/Paludis/AVR_Crossdev#Post-install
+[bug147155]: https://bugs.gentoo.org/show_bug.cgi?id=147155
+
+[[!tag tags/C]]
+[[!tag tags/hardware]]
+[[!tag tags/linux]]
+[[!tag tags/programming]]
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