I'm building a SCPI electronics lab instrument for Linux.

In this post I'm creating a service wrapper and install the Linux service.

It will start at Pi startup, and can be stopped / started as you'd expect from a service.

 

Prerequisites

 

You should have built the two binaries for this project, as documented in post 4a and 4b. If you didn't, the binaries are available as archive attached to post 4b.

linux_scpi_socket

linux_piface_digital_service_cpp

These binaries should be placed in /home/pi/bin, and made executable (chmod +x <binary_name>).

If you're using a recent raspbian (I use buster lite) there are no other dependencies.

 

Start and Stop Shell Scripts

 

I've created a startup and a shutdown shell script in that same /home/pi/bin directory, and made them executable (again using chmod +x <shell_script_name>).

 

scpi_face_start.sh

 

#!/bin/bash
echo "start piface. Wait 5 seconds to complete ..."
/home/pi/bin/linux_piface_digital_service_cpp 2223 &
sleep 5
echo "start scpi."
/home/pi/bin/linux_scpi_socket 2222 2223 &
echo "start sequence completed"

 

scpi_face_stop.sh

 

#!/bin/bash
killall -9 "/home/pi/bin/linux_scpi_socket"
killall -9 "/home/pi/bin/linux_piface_digital_service_cpp"

 

These scripts take care that the right order is used to start and terminate both executables.

There's a 5 second sleep to allow the piface binary to start its socket listening thread.

 

Both scripts will be invoked by the service handler to start and stop the daemon.

 

Service Script

 

Now the core of this post: creating that Linux service that starts up at boot, and can be restarted by the user.

I've used the raspbian networking.service as inspiration, and this website for the instructions: https://www.dexterindustries.com/howto/run-a-program-on-your-raspberry-pi-at-startup/

 

Create a new service wrapper in /lib/systemd/system, called scpi_piface.service.

 

sudo nano /lib/systemd/system/scpi_piface.service

 

Then enter this content:

 

[Unit]
Description=PiFace SCPI Service
DefaultDependencies=no
Requires=ifupdown-pre.service
Wants=network.target
After=local-fs.target network-pre.target apparmor.service systemd-sysctl.service systemd-modules-load.service ifupdown-pre.service network.target
Before=shutdown.target
Conflicts=shutdown.target
[Install]
WantedBy=multi-user.target
WantedBy=network-online.target
[Service]
Type=oneshot
#EnvironmentFile=-/etc/default/networking
ExecStart=/home/pi/bin/scpi_face_start.sh
ExecStop=/home/pi/bin/scpi_face_stop.sh
RemainAfterExit=true
TimeoutStartSec=5min
#User=pi

 

I've chosen to wait for the full network stack being up.

You have to mod the file attributes:

 

sudo chmod  644 /lib/systemd/system/scpi_piface.service

 

Then, tell systemd that there's a new configuration and tell it to enable the service:

 

sudo systemctl daemon-reload
sudo systemctl enable scpi_piface.service

 

If you reboot, the raspberry will start with the PiFace SCPI Service running.

 

Check:

 

 

Managing the Service

 

You can use the usual systemd commands to verify, stop and start the daemon.

 

sudo systemctl status scpi_piface.service
sudo systemctl stop scpi_piface.service
sudo systemctl start scpi_piface.service
sudo systemctl restart scpi_piface.service

 

 

related blog
SCPI on a Linux Board - Letter of Intent

SCPI on a Linux Board - Part 1: Proof of Concept

SCPI on a Linux Board - Part 2a: PiFace Digital C programming

SCPI on a Linux Board - Part 2b: PiFace Digital C++ programming
SCPI on a Linux Board - Part 3: TCP/IP Socket C++ programming
SCPI on a Linux Board - Part 4: TCP/IP SCPI and Instrument Service
SCPI on a Linux Board - Part 4b: TCP/IP SCPI and Instrument Service 100% Working
SCPI on a Linux Board - Part 4c: TCP/IP SCPI and Instrument Service - Run as a Daemon
SCPI on a Linux Board - Part 5a: LabVIEW Driver for LAB Switch: Open, Close and Switch functions