[linux-dvb] Question about dvb-usb driver stream settings

Patrick Boettcher patrick.boettcher at desy.de
Tue Sep 11 00:37:11 CEST 2007

Hi Tomi,

On Sat, 8 Sep 2007, Tomi Orava wrote:

> I've had quite a lot of problems with the existing Cinergy T2-driver
> (keyboard hangs sooner or later). Therefore I've converted the existing
> driver to use dvb-usb framework as used in the vp7045-driver. The current
> version of the converted driver seems to work OK, although the remote
> controller code has been disabled for now.
> I'm still wondering about the stream-settings and especially if there
> exists a predefined maximum value for the stream count-setting ?
> If I use too large value in here, the module will load & initialize just
> fine but will crash in unregistering phase when unloading.
> .stream = {
> 	.type = USB_BULK,
> 	.count = 7,
> 	.endpoint = 0x02,
> 	.u = {
> 		.bulk = {
> 			.buffersize = 4096,
> 		}
> 	}
> },
> The value 7 seems to work for the .count-variable, but
> when I was testing larger values (like 30) the module crashed the
> kernel in unloading phase:

The answer is simple, the maximum number of urbs you can have today is 10 
(see dvb-usb.h #define MAX_NO_URBS_FOR_DATA_STREAM 10 ) . Maybe a check 
would be appropriate.

However if you really have 4096 bytes urbs, 7 URBs should be enough on an 
average system (so far nobody ever had problems with streaming which were 
caused by too few URBs). 

Are you sure that the size of the URBs returned by the USB-stack is 4096? 
(load dvb-usb.ko with debug=0x100 and have a look at the lines "lengh 
<number>/4096" in syslog - it should be 4096 as <number>)


  Mail: patrick.boettcher at desy.de
  WWW:  http://www.wi-bw.tfh-wildau.de/~pboettch/

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