usbdump(8) question

[Hans Petter Selasky]

On Thursday 19 April 2012 21:34:54 Yuri wrote:
> I am trying to use usbdump(8) on one webcam, but the produced, log
> causes some questions.
>

Hi,
 
> 1. Why -s 1024 option doesn't show actual data even though SLEN for
> packets is non-zero?

The -s option must be set bigger than the maximum total data in a USB 
transfer, else you will only get parts of the data. Typical value: 65536

> 2. When I run webcamd, first 4 lines of log (with the error) quickly
> appear. Webcamd exits quickly, in 0.035s, but usbdump after 1-2 secs
> shows the rest of the log. Why is this significant delay? Why the first
> 4 lines aren't delayed?

Because usbdump uses a big buffer, which is only returned when it is filled up 
or when a 1 second timeout triggers.

--HPS