[linux-dvb] Question about Frontend performance (TDA10046 + TD1316)

Hartmut Hackmann hartmut.hackmann at t-online.de
Wed Aug 16 23:50:11 CEST 2006


Hi,

Chun Chung Lo wrote:
> Hi all,
> 
> I am now working on a DVB-T STB projects. SAA7130HL + TDA10046A + TD1316
> is used.
> 
> Previously I have made some tests on our STB. The TDA10046 + TD1316
> status are monitored during all the tests performed, by using the 'tzap'
> utilities (bundled in linuxtv-dvb-app-1.1.1)
> 
> Different degrees of corrupted TS is captured (a TS-to-PES software is
> used to runtime convert the catpured TS to a normal mpeg2 movie).
> 
> There are different fields can be monitored by using 'tzap', such as
> Signal Strength, SNR, BER, UNC, etc ... And I would like to know the
> following things:
> 
> 1. All tests has a zero UNC, but a little BER is recorded (about 120 out
> of 128K). Will this is the main reason of the corrupted TS?
> 
I can't tell right now how these values are scaled. UNC stands for
uncorrected blocks while BER stands for the raw bit error rate.

> 2. When BER > 0, is this means there exists some corrupted TS packets?
> If no, what does BER > 0 means (under this circumstance)?
> 
It depends on the DVB configuration, but to my experience in Germany, you
are fine as long as BER is less than ~4500 (and UNC is 0)

> 3. When UNC or BER (or both) > 0, will this means the discontinuity of
> the TS stream?

yes.
> 
> 4. Or the corruption of the captured TS is due to insufficient
> processing speed of the driver? (DMA? Buffers processing?)
> 
There was a bug in the transport stream capture (saa7134-ts.c) i fixed
11 months ago. If your driver is older, you need to update it.
Processor load is low if you just capture the stream.
But a problem might be that IDE DMA is not working properly on your
system. This might cause high latencies in the kernel and thus data loss.

> 5. Will the TS stream BW (or other settings) affect the capture
> performance? (I do not know but I have tried Test A and B several times
> and the result are quite coherent, as stated above).
> 
If you use wrong parameters for the channel decoder, it will not lock in
most cases. But what about the code for the TD1316? Where does this come
from? do you have a TD3116A or do you use some seperate IF amplifier?

> Please help and thank you for your attention.
> 
> Best regards,
> Lo Chun Chung
> 
Hope this helps

Hartmut



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