Reading pisound button state fro c program

Pisound
1

My setup is a raspberry Pi5 with a pisound board.

I am trying to get access to use the state of the pisound button from a c++ code program using the gpiod library. Here are the steps I have taken:

*I modified the pisound-btn.service with ExecStart=/usr/bin/pisound-btn --gpio21
*I added gpio=27=pu and gpio=17=pu to the /boot/firmware/config.txt file
*Using gpiod I set up pin 17 as an input (as I have many times for other gpio pins)

But when I try and read the pin 17 state using gpio_line_get_value it continuously reads as -1.

Am I missing something?

Thanks for your help.

2

Disable the pisound-btn service so the pin is not reserved (in use) by it and look at its source code for inspiration:

https://github.com/BlokasLabs/pisound/blob/master/pisound-btn/pisound-btn.c#L34

No need for changes in config.txt.

3

Thanks for the quick reply.

Clarification please - to disable the pisound service do you mean commenting out the pisound-btn.service file contents?

Thanks again.

4

You can use systemctl to manage the various systemd services, do:

sudo systemctl disable --now pisound-btn.service

The --now argument is a little shortcut to avoid having to explicitly run

sudo systemctl stop pisound-btn.service

Enabled units auto start on system startup, but you can stop and start them manually as desired.

5

So thank you again, this does allow me to enable and disable the pisound-btn service. Systemctl status shows that it is working to disable/enable the service.

What I am confused by, however, is that with the pisound-btn service ENABLED, shouldn’t I read 3.3v on one of the pins of the pisound button physical pin that connect to the PCB? I am reading 0v on all four of the pushbutton pins on start up with the pisound-btn.service enabled.

6

A service being Enabled does not necessarily mean that it is Running. When a service is Enabled, it means that it will start automatically on system boot up.

You are right about the GPIO pull-up - there should be a ~3.3V reading on one pair of the pins of the button, and the pisound-btn does request the GPIO pull-up to be enabled. If it’s not, either pisound-btn is not running (check if the process exists by running ps -e | grep pisound-btn), or you have modified the default configuration somewhere.

Otherwise, if everything is in the default state and running, and the GPIO pin is still not pulling up, it might be a damaged GPIO pin on the Raspberry Pi itself.