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.
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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;
}
}
}
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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