Broadcom 3510 was Re: [linux-dvb] Question regarding Air2PC r3 (Nxt2002 based)...answer may have implications for Nxt200x driver

CityK CityK at rogers.com
Tue Nov 29 19:27:50 CET 2005


Boleslaw Ciesielski wrote:
> Patrick Boettcher wrote:
>>>> Anyways, the r3 does demodulate QAM -- you can read about some user 
>>>> experiences here: 
>>>> http://www.avsforum.com/avs-vb/showthread.php?t=509869
>>>>
>>>
>>> In regards to the Broadcom 3510 based Air2PC r0.2 card still selling 
>>> on ebay, it appears from the Broadcom product brief 
>>> (http://www.broadcom.com/collateral/pb/3510-PB05-R.pdf ) that it 
>>> should be able to handle demodulation of a QAM source.  Anyone know 
>>> of any show stoppers that might prevent that from being realized? 
>>> (Patrick?)
>>
>>
>> Maybe it is working with QAM64, I just tested it with QAM256 and 
>> there was a unreasonable high error rate.
>>
>> BBTI told me that there are some hardware problems (either in the 
>> demod or in the tuner not being able to shift QAM-signals correctly 
>> to IF) which prevent the device from being used with QAM.
>
> Yes, and this also applies to the nxt2002 based Air2PC. See
>
> http://www.gossamer-threads.com/lists/mythtv/dev/120371
>
> There are some people who have it working but that's a small minority. 
> For most people QAM is a no go and it does seem like a hardware issue. 
> (Could it be QAM64 vs QAM256?)
>
> OTOH, the new lgdt3303 based card works beautifully with QAM.

Yes, thank you for that link Bolek.  I recently came across it myself in 
my quest to find out about the alleged problem with the Nxt2002.

I find it quite surprising that BBTI gave Patrick more or less the same 
reason regarding the Broadcom 3510 based Air2PC as they gave Taylor in 
regards to the Nxt2002 based Air2PC. 

Anyways, my original line of questioning about the Nxt2002/Air2PC was 
spawned by a discussion on AVS (starting here: 
http://www.avsforum.com/avs-vb/showthread.php?p=6416440&&#post6416440) 
about the the lack of QAM functionality in the MDP-120/Nxt2002.  Kei 
Clark responded that MIT had informed them (Digital Connection) that it 
had to do with a lack of memory on board. (I also vaguely recall the 
late Cliff Watson having once related that too....The point here is 
that, obviously, I wasn't the only one wondering why such demodulation 
capability hadn't ever been implemented on the MDP-120).  Now, I 
initially took Kei's comment to imply that it was in relation to the 
amount of onboard RAM used in assistance for mpeg decoding, but quickly 
discovered that wasn't the case, and it was Andrew Reynold's later 
comment that made me clue into that it is probably the demodulator's 
internal SRAM that is the limiting factor.

And finally tying all of this thread together -- my initial comment 
about "implications for the Nxt200x driver" was based on the thought 
that, if the Nxt2000 and Nxt2002 differ from the later Nxt2004 by way of 
internal SRAM configuration, then perhaps this should be accounted for 
in the unified driver.

We know the Nxt2002 can perform QAM, just not 100% reliably.  I suspect 
that MIT, being fully aware of the limitations imposed by the Nxt2002's 
internal SRAM configuration, reasoned not  to release drivers that 
supported  such function and instead just provided an OTA solution.  So, 
it is with this thought in mind, I suspect that as the (recently 
resumed) MyHD driver progress, that project will discover that it can 
provide QAM functionality for the MDP-120 under Linux....albeit, not a 
100% reliable solution, given the limitation of the demodulator.

Thoughts on my speculation are welcomed.

-- Cheers, CK





 



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