PX4/Firmware — pull request #374 by julianoes (2013-09-02 16:46:00+00:00)
Title: Allow mixer upload when PWM is on

This solves the bug:

mixer rejected by IO
mixer: error loading mixers from /etc/mixers/FMU_quad_x.mix: Invalid argument

Since the outputs are "armed" when after an idle PWM is sent, the mixer wont arrive. Therefore I think it makes more sense to check if the safety is off or not.