Hello every one.i am in a trouble and could anyone help me figure out ?

I have spent couple days trying to understand ,but I do not know the pricinple clearly which decides how to adjust the hw_ptr in the interrupt routine.

Below is the reference sourcecode in the snd_pcm_update_hw_ptr0().

When the DMA interrupt ocurrs the process will enter the snd_pcm_update_hw_ptr0() with the in_interrupt=1.

==========================================================

if (in_interrupt) {

/* we know that one period was processed */

/* delta = "expected next hw_ptr" for in_interrupt != 0 */

delta = runtime->hw_ptr_interrupt + runtime->period_size;

if (delta > new_hw_ptr) {

/* check for double acknowledged interrupts */

hdelta = jiffies - runtime->hw_ptr_jiffies;

if (hdelta > runtime->hw_ptr_buffer_jiffies/2) {

hw_base += runtime->buffer_size;

if (hw_base >= runtime->boundary)

hw_base = 0;

new_hw_ptr = hw_base + pos;

goto __delta;

}

}

}

==========================================================

The question is:

what can we get from the result of the compare between delta and new_hw_ptr.? Why we can conclue it?

The delta represent the expected location in the range of *boundary* , and it producted based the hw_ptr_interrupt(*not fixed*) and perod_size(fixed)?

The new_hw_ptr is producted by runtime->hw_ptr_base plus pos.

What Is the relationship between delta and new_hw_ptr? Why we can compare them with each other ?

Any tips will be ok.

Thanks a lot.

Best Regards

zw