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cx18: ATSC status

 

 

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jac1dlists at gmail

Apr 12, 2009, 6:04 PM

Post #1 of 4 (2420 views)
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cx18: ATSC status

Hi Andy,

I'm in the process of packing up and moving house at the moment, should be
resettled some time at the beginning of July.

Unfortunately, my test units are going to be packed away soon.

I am moving from a non-ATSC area in to an ATSC available area. I was
wondering if you might be able to provide a summary of the current ATSC
support in the chip. A few questions about it.

-Is the configuration process as simple as scanning for channels and then
selecting one via a v4l-ctl (if working from the command line)?

-Is the simultaneous capture from the analog input and the ATSC input
working in a stable fashion?

-What is the highest bitrate you have seen on the ATSC input?

-Are you aware of any problems with 2 x analog + 2 x ATSC capture on the
same PCI bus?

-Any antennas you have had particularly good luck with (or anyone else who
wants to chime in)?

-Is there any support for breaking out guide data that may be in the ATSC
TS?

-Any other things a new user might benefit from?

Thanks again for all your work on the driver.

We have a patch we hope to give you soon around the volume level
calculations for the RF input, we think we found a math bug there. Also,
we're still searching for an indication in the docs that the audio path on
the SA input should be able to be volume controlled. Thinking it through it
seems like it would be but we've seen no sign of it so far. Perhaps it is
meant to be line level locked?

-Jeff


jra at baylink

Apr 12, 2009, 7:41 PM

Post #2 of 4 (2279 views)
Permalink
Re: cx18: ATSC status [In reply to]

--- "Andy Walls" <awalls [at] radix> wrote:
> On Sun, 2009-04-12 at 21:04 -0400, Jeff Campbell wrote:
> > -Is the configuration process as simple as scanning for channels and
> > then selecting one via a v4l-ctl (if working from the command line)?
>
> No. You've got to build a scan file for your cable provider or OTA
> locality.

And you might find something of use here:

http://www.mythtv.org/wiki/Working_QAM_cable_layout

(If not, feel free to contribute)

> > -Any antennas you have had particularly good luck with (or anyone else
> > who wants to chime in)?
>
> In the US, most stations are digital on UHF freq's. Once the DTV
> cutover is complete, some stations will migrate back to their VHF
> assignments.

But many won't. WGBH-TV ch 2 in Boston, for example, will remain on UHF/19,
and merely PSIP back to "Channel 2"... thus making another mapping "'channel
number' to frequency band, and thus antenna" useless.

Cheers,
-- jra
--
Jay R. Ashworth Baylink jra [at] baylink
Designer The Things I Think RFC 2100
Ashworth & Associates http://baylink.pitas.com '87 e24
St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274

Start a man a fire, and he'll be warm all night.
Set a man on fire, and he'll be warm for the rest of his life.

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awalls at radix

Apr 12, 2009, 8:20 PM

Post #3 of 4 (2297 views)
Permalink
Re: cx18: ATSC status [In reply to]

On Sun, 2009-04-12 at 21:04 -0400, Jeff Campbell wrote:
> Hi Andy,
>
> I'm in the process of packing up and moving house at the moment,
> should be resettled some time at the beginning of July.
>
> Unfortunately, my test units are going to be packed away soon.
>
> I am moving from a non-ATSC area in to an ATSC available area. I was
> wondering if you might be able to provide a summary of the current
> ATSC support in the chip.

ATSC and North American QAM works for the HVR-1600.

Support for digital TV for other cards could be added given sufficient
information. All other CX23418 based cards I know of are DVB-T.


> A few questions about it.
>
> -Is the configuration process as simple as scanning for channels and
> then selecting one via a v4l-ctl (if working from the command line)?

No. You've got to build a scan file for your cable provider or OTA
locality.

For OTA ATSC on Fedora, I use this:

$ scandvb -A 1 -v -a 0 /usr/share/dvb-apps/atsc/us-ATSC-center-frequencies-8VSB > channels.conf

Note, Fedora renamed the scan command. Note you also need a file list
with frequencies to scan (which should come with your scan command app).


> -Is the simultaneous capture from the analog input and the ATSC input
> working in a stable fashion?

Yes.


> -What is the highest bitrate you have seen on the ATSC input?

ATSC has a fixed bitrate overall: ~19.(mumble) Mbps. The resolution of
the programs on the multiplex depends on how much the broadcaster wants
to stuff in that 19.x Mbps.


> -Are you aware of any problems with 2 x analog + 2 x ATSC capture on
> the same PCI bus?

No. It should work, but I have never tried it. Brandon Jenkins on the
LMML has 3 HVR-1600s in a box.

I have a set of "performance" improvement patches in the works for the
cx18 driver that I'll be pushing out soon. They remove all sleeps
(schedule()'s due to mutex_lock() acquisition delays or wait_event()'s
for ack IRQ's from the firmware) on the applications' read() paths or
when shuffling incoming buffers around. I also created more granular
queue locks for higher concurrency.

Those all certainly improve single card live playback performance. I'm
not sure how well it will scale, before it will fallback to
wait_event()'s in the applications' read() paths or when shuffling
incoming buffers. But it does gracefully fallback.


> -Any antennas you have had particularly good luck with (or anyone else
> who wants to chime in)?

In the US, most stations are digital on UHF freq's. Once the DTV
cutover is complete, some stations will migrate back to their VHF
assignments.

Basically a good VHF/UHF antenna for your needs. If you're close in, an
omni, or small directional, that you can easily rotate, will be fine.
Farther out, you'll want one with higher directivity.

Good cables: RG-6/U quad-shield.

Good grounding of the coax shield near the antenna to earth ground, to
reduce EMI and provide some lightning protection.

Proper splitters and terminators everywhere in your distribution plant.

A VHF/UHF amp from Winegard. Not more gain than you need though. Too
much gain and you'll overdrive the front end of your tuners, creating
intermodulation products and essentially raising your noise floor.

Keep the antenna far away from any source of VHF/UHF EMI from home
electronics. PC's have square waves that have fundamentals and
harmonics that land right in UHF.


> -Is there any support for breaking out guide data that may be in the
> ATSC TS?

MythTV can do it.


> -Any other things a new user might benefit from?

dvbsnoop is somewhat interesting, but is limited in decoding a TS in
places.

femon is useful.

dvbtraffic may be useful to you.


> Thanks again for all your work on the driver.

You're welcome.


> We have a patch we hope to give you soon around the volume level
> calculations for the RF input, we think we found a math bug there.

Hmm. I went though them once and found they were OK.

(My wife just helped me find my notes.) I have these equations scrawled
down:

V = (((114 * 2) - r) / 2 + (-96 - -114 + 1) + 4) * 512

r = -((V / 512 - (-96 - -114 + 1) - 4) * 2 - (2 * 114))

Which IIRC converts between the volume control value to the register
value.

The 9 LSBits of the V4L2 volume control are ignored/insignificant when
setting the CX23418 volume: that's the 512.

I recognize the 4 dB fudge factor.

-96 dB is the low end of the CX23418 audio vol control
-114 dB is the low end of the MSP3400 vol control

18 dB is the high end of the CX23418 audio vol control, so that's 18 -
-96 = 114, 1 dB steps or 228, 1/2 dB steps (of course the 0 dB value
seems to have been forgotten in that calculation, I'll have to double
check those steps.)

Bah, I'll have to double check it all....



> Also, we're still searching for an indication in the docs that the
> audio path on the SA input should be able to be volume controlled.
> Thinking it through it seems like it would be but we've seen no sign
> of it so far. Perhaps it is meant to be line level locked?

The last idea I had was that it was hard-routed through path 2 of the
baseband processing. Experimentation revealed to me, that this was not
the case. I'm pretty much resigned to setting up the CS5345 to do the
volume control for line-in. I just need to get it done.

Regards,
Andy
>
> -Jeff



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awalls at radix

Apr 13, 2009, 4:20 AM

Post #4 of 4 (2270 views)
Permalink
Re: cx18: ATSC status [In reply to]

On Sun, 2009-04-12 at 22:41 -0400, Jay R. Ashworth wrote:
> --- "Andy Walls" <awalls [at] radix> wrote:
> > On Sun, 2009-04-12 at 21:04 -0400, Jeff Campbell wrote:
> > > -Is the configuration process as simple as scanning for channels and
> > > then selecting one via a v4l-ctl (if working from the command line)?
> >
> > No. You've got to build a scan file for your cable provider or OTA
> > locality.
>
> And you might find something of use here:
>
> http://www.mythtv.org/wiki/Working_QAM_cable_layout
>
> (If not, feel free to contribute)
>
> > > -Any antennas you have had particularly good luck with (or anyone else
> > > who wants to chime in)?
> >
> > In the US, most stations are digital on UHF freq's. Once the DTV
> > cutover is complete, some stations will migrate back to their VHF
> > assignments.
>
> But many won't. WGBH-TV ch 2 in Boston, for example, will remain on UHF/19,
> and merely PSIP back to "Channel 2"... thus making another mapping "'channel
> number' to frequency band, and thus antenna" useless.

Right. That's what they do now. Gotta keep that "channel branding".

The offical plan for 1st and 2nd round designations is here:

http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-06-1082A2.pdf

In the Washington DC area,

WRC-TV moved has analog on 4 and digital on 48 and are going to stay at
48 (a loser move as far as propagation goes, due to free space path
loss).

WJLA-TV moved has analog on 7 and digital on 39 and are moving their
digital channel back down to 7. I'll have to rescan my channels on my
digital TV's then. (Most consumers may think that digital "channel 7"
turned off if they had it programmed pre-cutover.)


What's really fun is that, sometimes, when I do a channel scan and the
signal is weak, a TV or STB doesn't get the PSIP info correctly and I
get a bogus duplicate.

On my Sony TV right now I have a channel 50.1 and a channel 53.1 that
are the same digital broadcast. Analog channel 50 has DTV on analog
channel 53 with PSIP info saying it's "channel 50". One time my TV got
the PSIP data correctly and one time it didn't.

What a mess...

Regards,
Andy

> Cheers,
> -- jra


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