Andy,
Thanks for these changes. I've been trying various combinations with no success so far.. :(
will do some more testing tomorrow.
thanks
Tom
-----Original Message-----
From: ivtv-users-bounces@ivtvdriver.org on behalf of Andy Walls
Sent: Sat 8/1/2009 12:30 AM
To: User discussion about IVTV
Subject: Re: [ivtv-users] cx18: horizontal sync issue with analog composite 1 input
On Thu, 2009-07-30 at 11:42 -0400, Tom Ryan wrote:
>
> On 7/30/09 7:38 AM, "Andy Walls" <awalls@radix.net> wrote:
>
> Since, I've now implemented 1 custom control, adding more
> should be
> pretty easy. Give me a few days, and I should have something
> for you to
> play with.
Tom,
OK. I've got about 14 or so new user controls in the cx18 driver at
http://linuxtv.org/hg/~awalls/v4l-dvb They are:
extra_12db_gain (bool) : default=0 value=0
Use this if you suspect a weak signal. Since these are locally
connected cameras on 24 VAC with hopefully a short cable run for
testing, I doubt you need this,
luma_droop_compensation (bool) : default=0 value=0
chroma_droop_compensation (bool) : default=0 value=0
If you enable these, they will turn on impedance boosting for CVBS/Y and
C/Pr/Pb respectively. You would use these, if you had a cable or a
source that wasn't 75 ohms or some ohter reason for a bad impedance
match. This setting can cause the signal to get a DC offset, on the
boards, so if you use this, you should also use clamping (see below)
luma_clamping (bool) : default=0 value=0
This will enable clamping of the CVBS/Y sync tip to a specific analog
voltage level that should be below the midcode output level of the ADC.
This will remove positive DC offset, but can also give very weak signals
a negative DC offset in manual mode (see below). You should probably try
this setting. You likely have to use this setting if droop compensation
is enabled.
chroma_clamping (bool) : default=0 value=0
This will enable claming of the C/Pr/Pb signal voltage to 0 V, the ADC
midcode clamp level. This doesn't matter for your security camera.
auto_luma_clamping_level (bool) : default=1 value=1
When luma_clamping is enabled and this setting is enabled, the CX23418
will attempt to automatically adjust the sync tip clamping level for
you. You will want to leave this set at automatic when you first enable
clamping, to see if the CX23418 can do the work for you. If not, turn
it off, and set the clamp level manually (see below).
luma_clamping_voltage (menu) : min=0 max=7 default=0 value=0
0: -1.05 V
1: -0.8 V
2: -0.606 V
3: -0.460 V
4: -0.348 V
5: -0.264 V
6: -0.2 V
7: 0 V
This lets you manually set the luma sync tip clamping level to some
voltage below the midcode point (0 V) of the ADC. You must turn luma
clamping and turn off auto luma clamping level for this to be control to
be effective. Setting the sync tip clamp to 0 V will for sure be
useless. In my mind, the lower the voltage the better.
auto_digital_gain_control (bool) : default=1 value=1
digital_gain_level (int) : min=0 max=4095 step=1 default=256 value=1092 flags=slider
These control the digital front end gain that are applied digitally
after the analog gain stages and the AGC. This gain level is a rather
fine adjustment. There probably not much point on setting this to
manual and fine tuning the digital front end gain, unless you've already
done a manual setting of the analog front end gain first (see below).
auto_analog_gain_control (bool) : default=1 value=1
analog_gain_level (int) : min=16 max=248 step=1 default=64 value=32 flags=slider
This gain controls the analog stages before the ADC. You have to take
it out of auto before your manual gain setting will take effect. The
extra 12 dB gain stage comes before this one (in case you had it enabled
for a very weak signal).
sync_tip_height (int) : min=0 max=255 step=1 default=220 value=220 flags=slider
This is the height of the sync tip the timing circuitry is expecting or
the AGC circuitry is aiming to achieve (I'm not sure which, maybe both).
I don't know what the unit are.
auto_sync_height_crush (bool) : default=1 value=1
This control lets the digital front end adjust the sync_tip_height
register downward, if a sync signal comes in that exceeds the range of
the AGC. I;m not sure what the consequences are of turning it off.
I've never seen mine adjust the sync_tip_height (not that I've looked
alot).
sync_acquired_error_threshold (int) : min=0 max=255 step=1 default=16 value=16 flags=slider
sync_lost_error_threshold (int) : min=0 max=255 step=1 default=32 value=32 flags=slider
These two are sync tracking lock declaration thresholds. If the
measured sync signal is within the acquired error of the sync tip
height, lock is declared. If the measrued sync signal is outside of the
lost error tolerance, then the sync circuitry will delare sync was lost
and begin a search algorithm.
Note that the difference in values gives you some hysteresis. For
meaningful operation, the acquire error threshold must be less than the
lost error threshold.
>
> Thanks very much! I am trying to track down an oscilloscope (would a
> video of the output suffice?)
Yes, actaully a picture would do. I'd need to see the voltage levels
relative to 0 V, the shape of hysnc tip, some of the active video, and
I'd need the time scale too.
I'll need to knwo how the measurement was taken:
1. clipped to the cable ground and probe tip on the cable center pin
with no load
2. a 75 ohm resistor connected from cable center pin to ground, and the
signal measured across the resistor
3. the camera connected to the HVR-1600 with a 75 ohm T connector
located close the HVR-1600 end, with the measurement made from the
center pin and ground of the open T.
> and I would be willing to ship you one of the cameras if you're
> interested and these changes don't work out.
There are some more setting I have yet to program in as user controls.
The chip is extremely flexible. So I wouldn't want a camera sent jjust
yet. I also have very little time in the next month, so I'd prefer not
to have someone's equipment until I know I have time.
Regards,
Andy
> Let me know.
>
> Tom
>
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