unnamed user
What is Z-IDLE packet and how to change the Z-IDLE settings?
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Chris T
Z-idle packets are normal lift-off packets. In our Gen 4 touchpad, the number sent (currently 30) is configurable by setting register C2CA to the desired value. 
The purpose of sending 30 is to allow for using the packet rate to determine the speed of a double-tap event.  If double taps are not a feature you wish to use, you can safely reduce the number of packets.  We recommend having, at least, one z-idle packet as a deterministic way for knowing liftoff has occurred.  Otherwise, you can safely ignore the superfluous packets.
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mdl
As Chris describes, idle packets allow for the measurement of time.  When touch packets are reported, there is implicit timing--each packet means time has passed consistent with the packet rate.  Imagine if there were no packets at all reported when there is no touch.  There would be no way to disconnect one touch from another.  So at a minimum, there has to be a report that says "the finger went away."  It would be possible to measure the time between packets--if there is a local clock implemented--and guess whether an interruption is due to a liftoff, but there would always be risk that sluggish packet delivery might confuse things.  And finally, to determine double tap and drag (and other things like GlideExtend TM), there is a limit for time between a first and second touch.  It is easy to measure this time if it is just a specific number of packets.
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