[pvrusb2] Re: Problem with 20060102A

[Mike Isely]

On Tue, 3 Jan 2006, Ingo Flaschberger wrote:

> Hello,
>
> How long should switching "normally" need?
>
>
> bye,
> 	ingo flaschberger

There are no time delays or other arbitrary pauses in the pvrusb2 driver 
which might enforce some kind of minimal switching delay.  However I can't 
speak for the support modules and given the nature of the hardware there 
will certainly be some time delay.  For example, I2C transactions are 
proxied over USB and happen single-file - no pipelining.  I2C is already 
pretty slow and a channel change potentialy involves reconfiguring a lot 
of I2C controlled stuff.  So that can cause a delay.  Also the video 
hardware itself requires some time to lock onto the new channel - and then 
be noticed by the corresponding modules.

Finally I imagine that the mpeg2 encoder itself introduces latency as 
well.  In fact, if you run a normal TV right next to a pvrusb2-equipped PC 
and watch the same channel, I've actually see a 1-2 second latency in the 
video.

So it's hard to pin down what the maximum delay might be during a 
frequency change.  A second or so is probably not entirely unreasonable. 
There's not much that the driver can to do influence this, beyond not 
unnecessarily reconfiguring too much hardware when the frequency is 
changed.

   -Mike


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