Proposed fix for the suspend/resume pop

Mitch Bradley wmb at firmworks.com
Fri Mar 16 15:46:15 EDT 2007


I have a simple hardware fix for the popping sound that happens on power 
up, suspend, and resume.  The net component impact is the removal of one 
transistor.  I have tested this fix and it works.

Details are in  http://dev.laptop.org/ticket/977#comment:5

There is a software impact.  With this change, in order to get sound 
out, it is necessary to assert the EAPD pin on the CODEC.  That pin, 
deasserted by default, is nominally used to turn off the amp when 
asserted.  With the change, asserting that pin turns the amp on, not 
off.  Hardware engineers from Quanta and Analog Devices considered, 
without success, several other hardware changes to eliminate that pop.  
It boils down to the fact that we have either invert the sense of that 
pin, or switch the amp control to an entirely separate GPIO pin on 
another device (which are in short supply).

To assert that pin, write 0x8000 to codec register 0x26.



More information about the Devel mailing list