Re: [xine-devel] New fast DVB tuning method proposal

[Simon F. <sim...@on...>]

xi...@za... wrote:
>> Our channels.conf format is slightly extended to include tuning-time 
>> signal strength and SNR as the last two fields of each line (after the 
>> service ID). We have thus hacked out the offending code in our copy of 
>> xine, and mainline's tuning is now fast enough for our needs; the big 
>> slowdown is somewhere in kernel, where FE_GET_INFO is taking around 2 
>> seconds (but only if done shortly after opening the front-end device).
> 
> You can turn off some of the kernel silliness by invoking:
> 
> 	unsigned long mode = FE_TUNE_MODE_ONESHOT;
> 	ioctl(fd, FE_SET_FRONTEND_TUNE_MODE, mode);
> 
> But in any case you will find that bad things happen if you
> make your first status check too soon after tuning.
> Or if you make subsequent checks less than about 1 second apart.
> 
This is immediately after opening the frontend, before we've attempted 
to tune. Removing the error handling, the code (around line 600ish of 
input_dvb.c) looks like:

fd = open(frontend_device, O_RDWR);
ioctl(fd, FE_GET_INFO, fe_info_ptr);

If we put a sleep(10) between open and ioctl, there's no delay. If we 
don't, the ioctl takes around 2 seconds to return (currently acceptable 
for our use). The remainder of the mainline input_dvb code is plenty 
fast enough for us.
-- 
Any clues would be welcome,

Simon Farnsworth