[linux-dvb] Twinhan(chip 878) performance

Denys Fedoryshchenko nuclearcat at nuclearcat.com
Sat Jul 2 21:26:49 CEST 2005


Manu Abraham wrote:

> Denys Fedoryshchenko wrote:
>
>> I have read about Fusion / BT878 chip, and found that I2S bus can 
>> process only 40Mbps. This means transponders with stream rate higher 
>> than 40Mbps cannot be received? Or i am wrong?
>>
>
>
> It's not the I2S that is used but the GPIO on the Fusion that is used 
> to transfer data.
>
> But in any case, 40Mbps is too high a value for a complete 
> transponder. I don't know of any transponders of that bandwidth. 
> Moreover we are talking MPEG2 bandwidth. not uncompressed bandwidth. 
> So 40Mbps is quite large in that aspect ..
>
> An average transponder which has MPEG2 streams is about 27.5 Mbps 
> AFAIK. If i am not wrong .. I don't know about MPEG4.
>
> HTH
> Manu
>
As example
Yamal 201
C-Band
ISP Klassika
3980 L 38000 3/4

Symbolrate is important as i know for tuner module only, datarate of TS 
will be:

Grabbed from some website
So if we were to take a typical 38Mbps, QPSK, DVB carrier operating with 
¾ Viterbi and 188/204 Reed Solomon FEC, the symbol rate would be:
38.014706 * 204/188 * 4/3 *0.5 = 27.5 Msps

38000*2*3/4*188/204=52529 Mbit/s ?
And Twinhan/Vision able to receive it.
Also on another website in formula is 188-1... i dont know why.




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