Error in startup script in lockstep simulation with floating point PX4_SIM_SPEED_FACTOR

[fabianschilling]

Using a floating point PX4_SIM_SPEED_FACTOR as described in the Devguide (https://dev.px4.io/master/en/simulation/#simulation_speed) results in the following error:

INFO  [px4] Calling startup script: /bin/sh etc/init.d-posix/rcS 0
etc/init.d-posix/rcS: 165: etc/init.d-posix/rcS: Illegal number: 0.5
ERROR [px4] Startup script returned with return value: 512

The error is caused by performing calculations with built-in shell math (which only supports integer arithmetic) in lines 165, 169, and 173 in ROMFS/px4fmu_common/init.d-posix/rcS.

To reproduce, issue: PX4_SIM_SPEED_FACTOR=0.5 make posix gazebo . Setting PX4_SIM_SPEED_FACTOR to integer values results in the expected behavior.

A simple solution would be to use bc for both integer and floating point calculations in the rcS file.

[julianoes]

Thanks for the issue and fix!