Re: Topro 6800 driver

[Anders Blomdell <anders.blomdell@control.lth.se>]

Jean-Francois Moine wrote:
> On Fri, 27 Feb 2009 23:15:54 +0100
> Anders Blomdell <anders.blomdell@control.lth.se> wrote:
> 
>> Hi,
>>
>> I'm trying to write a driver for a webcam based on Topro TP6801/CX0342
>> (06a2:0003). My first attempt (needs gspca) can be found on:
>>
>> http://www.control.lth.se/user/andersb/tp6800.c
>>
>> Unfortunately the JPEG images (one example dump is in
>> http://www.control.lth.se/user/andersb/topro_img_dump.txt), seems to
>> be bogus, they start with (data is very similar to windows data):
>>
>> 00000000: 0xff,0xd8,0xff,0xfe,0x28,0x3c,0x01,0xe8,...
>> ...
>> 0000c340: ...,0xf4,0xc0,0xff,0xd9
>>
>> Anybody who has a good idea of how to find a DQT/Huffman table that
>> works with this image data?
> 
> Hi Anders,
> 
> Thomas Champagne (See To:) was also writing a driver for this webcam.
> Maybe you may merge your codes...
Thomas, if you have DQT/Huffman tables for this camera, please drop me a 
note.

> 
> About the JPEG images, the Huffman table is always the same 
Does this mean that it's the same for all JPEG images or only for one 
camera?

If it's the same for all images, it should mean that I have a way to 
determine how much I have to chop off after the 0xfffe tag (no illegal 
huffman codes -> possibly chop at the correct position).

Comments anyone?


 > and the
> quantization tables depend on the compression quality.
> 
> From the USB trace I had from Thomas, I saw that:
> 
> - when a packet starts with '55 ff d8', it is the first part of the
>   image. This one should start at the offset 8 of the packet.
> 
> - when a packet starts with 'cc', it is the next part of the image.
This is even in the docs, and is implemented in the driver.

> In the function pkt_scan, when finding the image start, you must add
> the JPEG header: 'ff d8', DQT, huffman table, SOF0 and SOS.
OK, will see if I can find the DQT (and possibly the Huffman table) in 
the windows driver (as suggested by Thomas Kaiser).

> As we don't know the quality used by the webcam, in my test repository,
> I added a control for that: the JPEG header is created at streamon
> time, and the quantization tables may be modified by the control on the
> fly (have a look at stk014.c for an example).
> 
> This solution is not the right one: the JPEG quality must be set by the
> VIDIOC_S_JPEGCOMP ioctl instead of VIDIOC_S_CTRL. I think I will update
> the concerned subdrivers next week.
I'll look into that monday.

> BTW, don't use the video4linux-list@redhat.com mailing-list anymore: all
> the video discussions are now done in linux-media@vger.kernel.org.
OK, so Google hit http://www.linuxtv.org/v4lwiki/index.php/Main_Page is 
no hit then...


Thanks

Anders Blomdell