Inappropriate ioctl on SPI when using launch, works using run

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Short version:

Calling the SPI transfer IOCTL works as intended if I run my code from ros2 run ..., but sets errno Inappropriate ioctl for device if I run the same node via ros2 launch ....

Longer version:

I have a Raspberry Pi 4, running RaspiOS 64 (Debian Buster), that's connected via SPI to a device I'm trying to communicate with.

I'm using the spidev userspace API and so for the transfers I'm calling the ioctl(fd, SPI_IOC_MESSAGE(dataSize), data). The code has several layers, but finally is wrapped into a rclcpp::Node and the first transfer is made right in the node's constructor.

The node is then instantiated in an executable consisting of a single-threaded executor running only one instance of this node class (and no other nodes).

My launch file is similarly simple, as it only gets the parameters file and calls the executable (via launch_ros.actions.Node). The parameters have the same exact values as the default ones declared in the node, and they don't matter for the SPI part of the code (only for a later values conversion etc).

The resulting behaviour is as described in the short version...

Links to the code:

• The launch file Note: for testing I've commented out the fan and the get_shutdown_on_exit parts
• The node code and the line triggering the error
• The device driver and the call to the transfer() function of a SPI wrapper
• The SPI wrapper and the ioctl that fails

Full log:

$ ros2 launch minirys_ros2 minirys_ve.launch.py
[INFO] [launch]: All log files can be found below /home/minirys/.ros/log/2021-07-24-16-51-28-489220-minirys-10602
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [motors-1]: process started with pid [10605]
[motors-1] [INFO] [1627138288.957487345] [minirys.motors_ve]: Got param: update period (s) 0.01
[motors-1] [INFO] [1627138288.958078059] [minirys.motors_ve]: Got param: stepsPerRevolution 200
[motors-1] [INFO] [1627138288.958214354] [minirys.motors_ve]: Got param: maxSpeed 6.28319
[motors-1] [INFO] [1627138288.958298315] [minirys.motors_ve]: Got param: acceleration 6.28319
[motors-1] [INFO] [1627138288.958402036] [minirys.motors_ve]: SPI: initializing
[motors-1] [INFO] [1627138289.058730929] [minirys.motors_ve]: SPI: initialized
[motors-1] [INFO] [1627138289.058942500] [minirys.motors_ve]: GPIO: initializing
[motors-1] [INFO] [1627138289.059062147] [minirys.motors_ve]: GPIO: initialized
[motors-1] [INFO] [1627138289.059134590] [minirys.motors_ve]: L6470: initializing
[motors-1] [INFO] [1627138289.170296198] [minirys.motors_ve]: L6470: resetting
[motors-1] terminate called after throwing an instance of 'std::runtime_error'
[motors-1]   what():  Error transferring via SPI: Inappropriate ioctl for device
[ERROR] [motors-1]: process has died [pid 10605, exit code -6, cmd '/home/minirys/minirys_ws/install/minirys_ros2/lib/minirys_ros2/motors --ros-args -r __ns:=/minirys --params-file /home/minirys/minirys_ws/install/minirys_ros2/share/minirys_ros2/config/params.yaml'].