Re: LinuxTV firmware blocks all wireless connections / traffic

[Antti Palosaari <crope@iki.fi>]

Devin Heitmueller wrote:
> On Thu, Sep 10, 2009 at 11:55 AM, Antti Palosaari<crope@iki.fi> wrote:
>> Devin Heitmueller wrote:
>>> The URB size is something that varies on a device-by-device basis,
>>> depending on the bridge chipset.   There really is no
>>> "one-size-fits-all" value you can assume.
>> I doubt no. I tested last week rather many USB chips and all I tested
>> allowed to set it as x188 or x512 bytes. If it is set something than chip
>> does not like it will give errors or packets that are not as large as
>> requested. You can test that easily, look dvb-usb module debug uxfer and use
>> powertop.
>>
>>> I usually take a look at a USB trace of the device under Windows, and
>>> then use the same value.
>> I have seen logs where different sizes of urbs used even same chip.
> 
> Yes, the URB size can change depending on who wrote the driver, or
> what the required throughput is.  For example, the em28xx has a
> different URB size depending on whether the target application is
> 19Mbps ATSC or 38Mbps QAM.  That just reinforces what I'm saying - the
> size selected in many cases is determined by the requirements of the
> chipset.

Yes thats just what I tried to say for. Look my previous thread where 
all currently sizes are listed. We need to define suitable values that 
are used. For example USB2.0 DVB-C, DVB-T, ATSC and same values for 
USB1.1 too. And stream size can vary much depending used transmission 
parameters too but I think such kind resolution logic is not needed.

Currently there is almost everything between 512 to 65k used for DVB-T 
that makes huge difference to load device causing.

Does anyone know if there is some table which says what are good USB 
transmission parameters for each bandwidth needed?

> Making it some multiple of 188 for DVB is logical since that's the
> MPEG packet size.  That seems pretty common in the bridges I have
> worked with.
> 
> Devin


Antti
-- 
http://palosaari.fi/