State machine loop state update issue

I’m reading firmware v0.5.4 source code and I have a question about state machine update.

I can’t find where the variable requested_state_ is updated other than in can_simple.cpp:

void CANSimple::set_axis_requested_state_callback(Axis& axis, const can_Message_t& msg) {

axis.requested_state_ = static_cast<Axis::AxisState>(can_getSignal<int32_t>(msg, 0, 16, true));


The state can also be modified through USB, UART and IIC, but I wonder where are the interfaces.