[alsa-devel] Query regarding pointer callback

Hi

In Writing an ALSA driver, it is said that pointer callback is called usually from the buffer-update routine in the pcm middle layer, which is invoked when snd_pcm_period_elapsed() is called in the interrupt routine. Then the pcm middle layer updates the position and calculates the available space, and wakes up the sleeping poll threads, etc

What are the other places from where pointer callback is called? If it is not called from any other routine then does it mean that interrupts are occuring?