[mythtv-users] Max number of IVTV cards

[Kaushik Mallick]

Thanks for all the help and support. I will try to add
one at a time and see what happens. Just to clarify
things, I am not planning on transcoding after
recording the channels. So hopefully I can get by with
one decent CPU for 5 cards. I do worry about the DMA
traffic.

Also I need to mention that I am happy with the mythtv
box I have for my living room. This particular system
I need to look at to record 5 channels simultaneously
is for a different venture altogether. I need to have
it in one box. I need to look for a 5 way splitter
too!


--- "Michael T. Dean" <mtdean at thirdcontact.com> wrote:

> On 08/19/2004 01:49 AM, Kaushik Mallick wrote:
> 
> >I want to build a system to record 5 tv channels at
> >the same time. I plan to use a ivtv card like
> >Avermedia M179 for each channel. Is there any limit
> on
> >maximum number of these cards I can use in a system
> >(besides the limitation of pci slots on my
> >motherboard)?
> >
> ivtv 0.1.9 supports up to 9 cards, but there was
> talk of reducing it to 
> 8 (and it may have happened for recent ck releases)
> because a) support 
> for more cards complicates the programming and b)
> the DMA traffic 
> generated by that many cards would probably kill any
> system in 
> existence.  (Note, also, that the value 9 was chosen
> arbitrarily.  PCI 
> buses can support more cards than that, and systems
> can have more than 
> one PCI bus--so it was already constrained at 9. 
> However, due to the 
> complexity of coding for an "unlimited" number of
> devices, drivers often 
> impose arbitrary (but sensible) limits.)  See the
> thread starting at 
> http://www.poptix.net/ivtv/Jun-2004/msg00888.html .
> 
> >Do I need more CPU power as the number
> >of channels I need to record go up? I am hoping
> >somebody have had run into a similar experience.
> >Thanks beforehand.
> >  
> >
> More than CPU power, you'll probably need luck. 
> Because the card is 
> doing the encoding on-board, the CPU gets almost no
> load.  However, the 
> system will have to deal with a significant amount
> of DMA traffic.  Some 
> chipsets can handle it.; others cannot.
> 
> However, if you're doing things like automatic
> transcoding or commercial 
> flagging after recording, you will need CPU power
> for that.  Basically, 
> if you have 5 channels recording and are
> transcoding/commercial 
> flagging, you'll either need to have a CPU (CPU's)
> that can 
> transcode/flag faster than you can record or offload
> flagging to other 
> systems (automatic transcoding currently cannot be
> offloaded).
> 
> Since the ivtv cards present so little CPU load, I
> would recommend 
> getting an old system and making a second (and
> possibly a third) 
> backend.  It will probably make your life much
> easier and your PVR much 
> more reliable.
> 
> HTH.
> 
> Mike
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