[vdr] power consumption, powertop and wakups per second with a af9015 device

Heinrich Langos henrik-vdr at prak.org
Wed Mar 18 12:54:24 CET 2009

On Mon, Mar 16, 2009 at 05:23:53PM +0200, Antti Palosaari wrote:
> Heinrich Langos wrote:
>> Anyway .. the main problem remains. 
>> Is there a tool that would only do some minimal actions on a dvb 
>> device? 
> Like power_on? femon for example reads device status. zap, scan...

I cleaned up my system a little more to reduce the avg wakups per second.
Now, when vdr is not started I get about 5 wakeups per second and only
about 0.2-0.3% of the time is spent in C0 (cpu running).

Now starting "femon" I get the following outut at about one line per second:
| jukebox:/tmp/hgaf9015.MPZgGXIerw/af9015-a57ea2073e77# femon -H
| FE: Afatech AF9013 DVB-T (DVBT)
| status SCVYL | signal  18% | snr   0% | ber 0 | unc 6073 | FE_HAS_LOCK
| status SCVYL | signal  18% | snr   0% | ber 0 | unc 6073 | FE_HAS_LOCK
| status SCVYL | signal  18% | snr   0% | ber 0 | unc 6073 | FE_HAS_LOCK
| ...

The avg wakups per second go up to about 30, time spent in C0 is slightly
higher with 0.4 - 0.6%.

Now starting "zap" to tune into a channel:
| jukebox:/tmp/hgaf9015.MPZgGXIerw/af9015-a57ea2073e77# zap -channels /tmp/channel.conf N24
| Using frontend "Afatech AF9013 DVB-T", type DVB-T
| status SCVYL | signal 0000 | snr 0014 | ber 00000000 | unc 000017b9 | FE_HAS_LOCK

Now the wakups per second go up up about 3000 and the cpu is running in C0 
about 30% of the time!

I ran "dvbtraffic" (itself causing about 10 wakups but hardly any cpu load)
on another console to see what is happening and it seems like "femon" does 
only check the receiver's status while "zap" realy causes data to be transfered 
from the USB device to the host.

So the rather heavy load that I see with vdr is probably not caused by vdr
itself but by the USB data transfer. 

The new questions are:

Does every USB DVB-T receiver cause the same amount of cpu load?

Does vdr need to read the data stream all of the time? 
Can it be switched off? (At least while nobody watches and EPG data 
is not refreshed?)


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