Yaroslav Popovitch | 5 Oct 15:28 2003

HDCS1020 and TCTRL

Hi! I am writing driver for Logitech QuickCam Express camera: HDCS1020,
STV0602AA?, VENDOR_ID 0x046d, PRODUCT_ID 0x0870. Driver is partly based
on qce-ga-0.40c and qc-usb-0.5.1 drivers. There is initialization of TCTRL
register in "hdcs_init" functions of both drivers by used different
values:
- qce-ga driver uses 0x7e value
- qc-usb-0.5.1  uses 0x09 value

If I use 0x7e value then camera's picture is updated to slow, but I get
normal stream of frames.

If I use 0x09 value, then picture is updated fast, with low latency, but
stream of frames is broken. I cannot get the whole frame, its size is
changing in time.

Would you point to how to get low latency and normal stream of frames?

Cheers,YP

-
Mr. Yaroslav Popovitch yp <at> sot.com       - tel. +372 6419975
SOT Finnish Software Engineering Ltd.   - fax  +372 6419876
Kreutzwaldi 7-4, 10124  TALLINN         - http://www.sot.com
ESTONIA                                 - http://sotlinux.net

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(Continue reading)

Yaroslav Popovitch | 5 Jan 11:16 2005

Re: HDCS1020 and TCTRL

YO! 
I found the reason of problem. I was resubmitting the 
same urb from complete handler. Such approach did not allow to receive the 
whole frame on high speed. As result I was getting broken frames. 
Problem was solved when I started to use several urbs.
Congratulations !!!

NB! One another question related to QuickCam Express(STV060X/HDCS1020):
The configuration of iso. endpoint in altsetting 1 allows to have packets 
with maximum size 1023. But qc-usb driver sets STV chip to use 847. 
What is the reason for that? 

Cheers,YP

On Sun, 5 Oct 2003, Yaroslav Popovitch wrote:

> Hi! I am writing driver for Logitech QuickCam Express camera: HDCS1020,
> STV0602AA?, VENDOR_ID 0x046d, PRODUCT_ID 0x0870. Driver is partly based
> on qce-ga-0.40c and qc-usb-0.5.1 drivers. There is initialization of TCTRL
> register in "hdcs_init" functions of both drivers by used different
> values:
> - qce-ga driver uses 0x7e value
> - qc-usb-0.5.1  uses 0x09 value
> 
> If I use 0x7e value then camera's picture is updated to slow, but I get
> normal stream of frames.
> 
> If I use 0x09 value, then picture is updated fast, with low latency, but
> stream of frames is broken. I cannot get the whole frame, its size is
> changing in time.
(Continue reading)

Tuukka Toivonen | 5 Jan 11:40 2005
Picon
Picon

Re: HDCS1020 and TCTRL

On Wed, 5 Jan 2005, Yaroslav Popovitch wrote:

> The configuration of iso. endpoint in altsetting 1 allows to have packets
> with maximum size 1023. But qc-usb driver sets STV chip to use 847.

Because qce-ga did so and as far as I know it haven't caused the driver
not to work for anyone... so why to fix it if it isn't broken.

I suppose the original values comes from some w*ndows driver USB-logs.
But it might be some other camera like HDCS-1000 (I don't remember
what packet size it reported but possibly different).

Also, I suppose smaller packet size is better if it is sufficiently
large since then other USB devices presumable have more USB bandwidth.

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