When the driver turns off the ignition in a vehicle, display computers like terminals in harvesters or infotainment systems in cars should be notified. The display computers should save important data and shut down orderly.
When the display computer runs on Linux, it learns the status of the ignition by monitoring the GPIO for clamp 15. Linux writes the value of the GPIO to a special file in the sys filesystem. On one of my display computers, clamp15 is mapped to the special file
/sys/class/gpio/gpio72/value. When the ignition is on, this file contains the string “1”. When off, this file contains “0”. The number of GPIO (here: 72) varies from display computer to display computer.
On the Linux command line, we get the value of clamp 15 with this command:
$ cat /sys/class/gpio/gpio72/value 1
The command returns “0” when the ignition is off and “1” when it is on.
How can a Qt application monitor the status of the GPIO clamp 15 such that it can shut down orderly when the driver turns off the ignition?
Read More »Monitoring Sys Files with QFileSystemWatcher