[sane-devel] SniffUSB: URB direction and TransferFlags IN/OUT confusion

[Gernot Hassenpflug]

On Thu, Feb 25, 2010 at 1:05 AM, m. allan noah <kitno455 at gmail.com> wrote:
> Attached is a copy of a script I wrote that clears up these verbose
> logs. I don't know if it is the most recent version, I cannot reach my
> development machine, and i just found this copy with google :)

Thanks for that, I had seen it but since I haven't grokked the basics
yet, I was using the messy output.

> cat UsbSnoop.log | perl spike4.pl > UsbSnoop.out

Very nice & clean indeed.

I am still confused on the questions below, while reading more to see
if the answers appear:

>> 1) there are 4 endpoints:
>>    *　0x00000000 which has both IN and OUT version;
>>    *   0x00000007 which is a bulk type, seems to be for OUT only;
>>    *   0x00000088 which is a bulk type, seems to be for both IN and OUT;
>>    *   0x00000089 which is an interrupt type, seems to be for both IN and OUT.
>>   whereas I thought only endpoint 0x00000000 can have both IN and OUT
>> use, while all other endpoints are either IN or OUT, but not both.

Are endpoints apart from the default 0x00000000 able to have both IN
and OUT now? Or did I misunderstand the log file (and spike4 output
also)?

>> 2)  snoop headings like ">>>  URB 16 going down  >>>" and  "<<<  URB
>> 16 coming back  <<<" are both followed by:
>>      TransferFlags        = 00000002 (USBD_TRANSFER_DIRECTION_OUT,
>> USBD_SHORT_TRANSFER_OK)
>>     whereas I thought that "down" means the endpoint must be "OUT"
>> direction, and "back" must be "IN" direction.

So I expected a URB "coming back" to contain a TransferFlags with
DIRECTION_IN, but often it has instead DIRECTION_OUT. Is that
relevant?

>> 3) sometimes there is a value for TransferBufferLength but no apparent
>> data, like below (simplified using spike4 output):

Urb 6 (C) ep=7 (write) 193 ms

pause 0 ms

Urb 7 (C) ep=7 (write) 516 ms

I do not see (with my current knowledge) where the data is kept that
is written out to the device. Where should I be looking?

Regards,
Gernot Hassenpflug