px4fmu split safety button into new module

[dagar]

TODO:

• review PWM_SERVO_SET_FORCE_SAFETY_OFF/PWM_SERVO_SET_FORCE_SAFETY_ON
  - completely replace these IOCTLs with in_esc_calibration_mode
• test pixracer
• test nxphlite
• test pixhawk 4 mini

[LorenzMeier]

@bkueng Could you help to get this in? Thanks!

[davids5]

This good as an extract of the code from the FMU. Consider possibly Fix tabbing

Long term there should be board_read_saftey_switch() state or a macro that returns logic true when down.

As it is and since there is a led blinker the poling it fine but longterm
The switch code could be like TAP power button and use interrupts. Then the HP work can then just blink the lights by schedule the changes.

[bkueng]

Generally looks good, but there are several details that should to be improved.

[julianoes]

@dagar I'm fighting for all your PRs 😄.

[LorenzMeier]

What is required to bring this in in terms of review / testing?

[dagar]

Verified fmu-v4 behavior (with and without CBRK_IO_SAFETY set) matches master. I'll check fmu-v5 with and without an IO next.

[dagar]

Tested pixhawk 4 and 4 mini.

This mostly preserves the behavior in master, but gets the logic out of the pwm output module (px4fmu). The difference is that we still get safety button functionality independent of fmu running or mixers loaded.

@davids5 and I briefly discussed handling the button with gpio_setevent, but we can pursue that later.