I've got the following tricky problem: I'm using pin #22 (GPIO25) of my Raspi 3B as a GPIO input and read its state by using the pigpio function
gpioSetAlertFunc (25, relay::IgnitionISR), where
relay::IgnitionISR is a pointer to the function called when pigpio detects a state change. After adding a JustBoom DAC HAT sound card, the input kept on working, but once I started talking to the sound card by using the
out123_open (sound::mp3_output_handle, "alsa", NULL) function of the mpg123 library, I stopped receiving alerts from pin #22 without getting any error messages.
The pinout description of the sound card states pin #22 as optional (for use with an IR receiver). I don't have such a receiver soldered to the sound card, so that I don't really understand why the card interferes with a pin it isn't using anyway.
Low-level checks by using
gpio readall and
piscope did deliver correct resoluts: Once I pulled pin #22 to high, I received a 1, and a 0 when I pulled it to low.
Any hints? Thank you for any useful information.