[mythtv-users] Delay starting backend until initialisation of capture card(s)

[Jan Ceuleers]

Hi.

I am using 0.23-fixes and have recently moved a pvrusb2 device 
(Hauppauge HVR 1900) from my frontend/slave backend to the master 
backend. This latter machine is much faster than the former, and upon 
power-up it boots and starts the backend well before the tuner is fully 
up and running. As a result this tuner never gets used until I manually 
restart the backend process.

Judging by the logfile (excerpt inline below) it looks like a race 
condition whereby the /dev/video0 device node has been created (by 
udev?) but the permissions have not yet been set properly at the time 
that the backend tries to open it.

I could just insert a delay into the backend's startup script 
(/etc/init.d/mythtv-backend), although since my distro (Ubuntu 10.04) 
uses the event-driven upstart I'm not sure that this would work but I'm 
willing to try. Still, I'd be interested in any hints on how to do this 
properly:

- Which event should I make the backend wait for? According to dmesg the 
/dev/video0 device is registered 14.7 seconds after boot (dmesg 
attached), but an RF calibration process subsequently still takes place, 
resulting in a "DVB: registering adapter 0 frontend 0"... message only 
around 41.7 seconds after boot. I can see in /var/log/messages that 
these events are at some time before 11:33:01 and at 11:33:19 local 
time, respectively. The first of these times is just when the dmesg 
buffer gets sucked into syslog, so this time stamp is inaccurate. 
Anyway, the first event is before the backend starts, and the second 
event is after the backend's attempt to open the tuner.

- Is it possible to tell upstart that the mythtv-backend process should 
not be started until the above condition has been met?

If it makes any difference: this device is capable of both analogue 
capture and DVB-T. I am using it as an analogue tuner only.


Thanks, Jan




=== Backend log excerpt for case where tuner unable to be opened ===

2011-02-02 11:33:05.914 mythbackend version: branches/release-0-23-fixes 
[24158] www.mythtv.org
...
2011-02-02 11:33:09.839 Channel(/dev/video0)::Open(): Can't open video 
device, error "Permission denied"
2011-02-02 11:33:09.917 mythbackend: Problem with capture cards: Card 1 
failed init
...


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