On Do, 2016-08-25 at 20:27 +0200, Jörg Krause wrote:
Hi,
I am looking for a way to toggle a GPIO if ALSA is about to play or has stopped to turn an external amplifier on/off.
Can it be done using libasound or can I use a plugin or write one?
After having a long night digging through ALSA's sourced I got it working writing a PCM hook library. Basically, it does the following:
static int snd_pcm_hook_gpio_hook_close(snd_pcm_hook_t *hook) { int fd;
/* * Set GPIO LOW */
return 0; }
int _snd_pcm_hook_gpio_hook_install(snd_pcm_t *pcm, snd_config_t *conf) { int fd; int err;
snd_pcm_hook_t *h_close = NULL;
err = snd_pcm_hook_add(&h_close, pcm, SND_PCM_HOOK_TYPE_CLOSE, snd_pcm_hook_gpio_hook_close, NULL); if (err < 0) goto _err;
/* Init and set GPIO HIGH */
return 0;
_err: if (h_close) snd_pcm_hook_remove(h_close);
return err; } SND_DLSYM_BUILD_VERSION(_snd_pcm_hook_gpio_hook_install, SND_CONFIG_DLSYM_VERSION_HOOK);
For reference my asound.conf:
pcm.softvol { type softvol slave { pcm "gpio_hook" } control { name "Master" card 0 } } pcm_hook_type.gpio_hook { lib "libasound_gpio_hook.so" } pcm.softvol_hook { type hooks slave { pcm "hw:0" } hooks.0 { type "gpio_hook" } }
Jörg