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I've made a program that communicates with hardware over CAN bus. When I start my program via CLI, everything seems to run fine, but starting the process via a Systemd service leads to paused traffic

I'm making a system that communicates with hardware over CAN bus. When I start my program via CLI, everything seems to run fine, I'll quantify this in a second. Then I created systemd services, like below, to autostart the process on system power up.

By plotting log timestamps, we noticed that there are periodic pauses in the CAN traffic, anywhere between 250ms to a few seconds, every 5 or so minutes (not a regular rate), within a 30 minute window. If we switch back to starting up via CLI, we might get one 100ms drop over a 3 hour period, essentially no issue.

Technically, we can tolerate pauses like this in the traffic, but the issue is that we don't understand the cause of these dropped messages (run via systemd vs starting up manually via command line).

Does anyone have an inkling what's going on here?

Other notes: - We don't use any environment variables or parameters (read in via config file). - We've just watched CAN traffic with nothing running, no drops, so we're pretty confident it's not our hardware/socketCAN driver - We've tried starting via services on an Arch laptop and didn't see this pausing behavior.

[Unit]
Description=Simple service to start CAN C2 process 

[Service]
Type=simple
User=dzyne
WorkingDirectory=/home/thisguy/canProg/build/bin
ExecStart=/home/thisguy/canProg/build/bin/piccolo
Restart=on-failure 
# or always, on-abort, etc
RestartSec=5

[Install]
WantedBy=multi-user.target

I'd expect that no pauses between messages larger then about ~20-100ms, our tolerance, when run via system service

abdomo
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  • This might be because something, required by socketCAN, isn't ready when you start your process. Did you had a look at `sudo systemctl status myservice` ? If the problem isn't observed when you manually restart the service after the boot process, it would be a indicator for this issue. – Benoît Jun 25 '19 at 07:15
  • Linux isn't a RTOS so what makes you think it will behave deterministically real-time-wise? Sounds like the PC is stalling, doing something unrelated. – Lundin Jun 25 '19 at 10:45

0 Answers0