Getting the cross-compilation toolchain for AVR configured on Gentoo to allow programming the Teensy 2.0 microcontroller..

My longest-running project to date: Make my own keyboard. The hardware involved has been through a couple of iterations, but now I've settled on the fairly common Teensy 2.0 as the controller. This document describes how to get the right toolchain configured on Gentoo. ## Overview 1. Install the cross-compiler and required packages 2. Install teensy\_loader\_cli 3. Compile and load fast morse-code blinky program ## Tooling on Gentoo First we need a C compiler. To program the Teensy 2.0 we need a cross-compiler for AVR. The official documentation page only describes setting up this toolchain on Ubuntu. On Gentoo, we have crossdev to help us out. To get an AVR cross-compiler toolchain, it's as simple as: $ crossdev -t avr It also turns out we need dev-libs/libusb-compat (for ``). ## Teensy loader CLI There is a graphical utility for flashing the Teensy, but I much prefer a command-line tool, and luckily there is one we can just use: teensy\_loader\_cli. Building the tool requires the `` header,On Gentoo this header is provided by dev-libs/libusb-compat but that should be all that's needed to run `make` successfully. To flash the sample slow blinking program on the Teensy 2.0, plug it in, press the push button so the light stops blinking, then run: $ ./teensy_loader_cli --mcu=TEENSY2 -v -w blink_slow_Teensy2.hex That should be all there is to it. ## Blinky The blinky program on the page (it's provided as a zip file) provides a larger program that blinks morse code. With avr-gcc version 13, the blinky sources do not compile out of the box. In usb\_debug\_only.c there is a collection of static global variables that are meant to go in read-only memory (by the `__attribute__((progmem))` attribute). The error looks something like this: error: variable ‘xyz’ must be const in order to be put into read-only section by means of ‘__attribute__((progmem))’ Adding `const` to these variables lets the program compile. The default settings in the Makefile target Teensy 2.0 so no further changes are necessary. To flash blinky.hex onto our Teensy 2.0 do: $ teensy_loader_cli --mcu=TEENSY2 -w -v blinky.hex And off we go!