[asterisk-dev] Hardwareless PCI Card Simulator

[Derek Smithies]

Hi,

On Tue, 9 May 2006, Hugo Saporetti Junior wrote:
> I would like to know if there's any software to simulate a PCI WCFXO
> card. If so, where could I download it? I want to use it with
> Zaptel/Asterisk. Regards
> 

This is one of those questions that has been posed many times in the past.
The typical answer is 
  "no, not possible" and "the timing won't allow it" etc.

These statements are correct, but I have yet to see an explanation of why 
the timing will not allow it.

The reason why no software to simulate a card is very simple:

 Every millisecond, there is one interrupt generated by the card. The 
driver has to collect 8 bytes for each active channel from the card.
Thus, it is not inconceivable for the driver to have to collect 240 bytes 
from the card every millisecond.

This places a noticable load on the PCI bus. With other activity on the 
bus (database acccess etc) you will get missed data transfers, and the 
audio quality will drop.

Current computers cannot (close, but not yet) simulate the one 
interrupt per ms. Once computers get another couple of orders of 
magnitude faster it may be possible. 

Derek.
-- 
Derek Smithies Ph.D.                 Any fool can write code that 
IndraNet Technologies Ltd.                a computer can understand.        
Email: derek at indranet.co.nz         Good programmers write code 
ph +64 3 365 6485                          that humans can understand.
Web: http://www.indranet-technologies.com/            Martin Fowler