[linux-dvb] Slow control data from dvb-usb (VP7045)

Manu Abraham abraham.manu at gmail.com
Mon Nov 28 10:12:37 CET 2005

Patrick Boettcher wrote:

> Hi Jeremy,
> On Mon, 28 Nov 2005, Jeremy Nysen wrote:
>> The control data requests for dvb-usb devices (I'm testing with a 
>> VP7045 device) is quite slow. Each request can take a few hundred 
>> milliseconds to complete and return data. This gets longer when 
>> multiple data bytes are requested from the frontend. eg. generating 3 
>> requests for 3 register bytes of AGC information for the MT352 in the 
>> device can take a whole second. If I perform 6 requests it takes 
>> twice as long.
> Reading the MT352 is an extension, which is (afair) not done in the 
> Windowsdriver made by Twinhan. Additionally I have a large msleep in 
> every read-function, because reads are failing "all the time". You can 
> try to reduce the read-delay in vp7045.c to an optimal value.

Hello Patrick,

Reads will fail, as does happen in the PCI version too. Rather than 
playing around with increasing/decreasing timeouts, this _is_ nonsense. 
The dst too suffered from this same illness off playing with transaction 
timings earlier and had unusually long delays. Asking end users to play 
around with the timings would generally cause confusion, and generally 
for each and every problem people would be fiddling with the timings,, 
which is _not_ the actual solution.

A better way would be _probably_ to handle the transaction errors 
accordingly. ie, if there is an error_condition, handle the error 
condition and retry the transaction. For the PCI cards, to identify 
these transaction errors i had put verbose messages for these operations 
such that people can report back on these, rather than hiding them. 
These debug messages can be used to fix the actual problems.


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