[linux-dvb] Re: Reading from 4 cards simultaneously?

[Johannes Stezenbach <js@convergence.de>]

Johann Hanne wrote:
> 
> i'm running a box (Pentium 3 800 MHz) with four DVB-budget-cards (2xDVB-S, 
> 2xDVB-C) with Kernel 2.4.24 and linuxtv-dvb-drivers 1.1.0. Everything (tuning 
> via the frontend device and reading of the TS via the dvr device) works fine 
> as long as I only read data from three cards simultaneously. As soon as I 
> open the fourth dvr device, the first dvr device does no longer give me data. 
> This behaviour is perfectly reproducable and does NOT depend on the dvb 
> device number, the data always stops coming in on the device which I have 
> OPENED FIRST. I.e. if I open /dev/dvb/adapter0/dvr0 first, I get no data from 
> it after opening the fourth device and the same happens 
> with /dev/dvb/adapter1/dvr0, if this one is opened first.

I think I've heard this before, but I've no idea what causes this. Maybe some
PCI limit (like one card's transfer times out because the others hog
the bus for too long). Have you tried to play with setpci?

> BTW: What's the correct way to increase the maximum number of supported DVB 
> devices (I'm using devfs)? I think the default number is still 4, and in an 
> earlier thread I noticed that incrementing MAX_NUM_DVB and 
> SAA7146_MAX_DEVICES did create more devices, but the drivers misdetected the 
> card types. Moreover these two defines seem to have gone in version 1.1.0.

With kernel 2.4 this would work with CONFIG_DVB_DEVFS_ONLY
(we would have to use a second major for non-devfs).

For 2.6 the new 32bit dev_t would allow more cards, but we
haven't changed device number allocation yet because it
breaks 2.4 backwards compatibility.


Johannes


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