Data path from TV tuner to VGA card

[Tom Del Rosso]

I'm wondering if a TV tuner with VGA on the same board (like ATI
All-in-Wonder) doesn't use the PCI bus to get the data to the monitor.

Would I be right to assume that separate tuner boards can't use bus
mastering to get the picture directly to the video card, and the video data
has to be processed by the CPU first?

The all-in-ones don't use any bus bandwidth for watching (not recording of
course), right?

I know the impact might be insignificant, but that's a separate question.
I still would like to understand how the things work, and how they use the
bus. Thanks.

 

[Paul]

I'm wondering if a TV tuner with VGA on the same board (like ATI
All-in-Wonder) doesn't use the PCI bus to get the data to the monitor.

Would I be right to assume that separate tuner boards can't use bus
mastering to get the picture directly to the video card, and the video data
has to be processed by the CPU first?

The all-in-ones don't use any bus bandwidth for watching (not recording of
course), right?

I know the impact might be insignificant, but that's a separate question.
I still would like to understand how the things work, and how they use the
bus. Thanks.

There is a block diagram here. The Theater chip connects to
the GPU, but what happens then is a mystery

http://www.xbitlabs.com/articles/video/display/aiw-9700-pro_4.html

If the GPU and Theater chip were generally available parts,
with spec sheets to match (like if Philips made them), we'd
get some solid technical info. With ATI, we have to rely on
marketing slides.

As for your question about separate tuner boards, at least the
BT848/BT878 family had an option to DMA to two separate
memory areas. You could DMA odd frames to say an area on
the video card frame buffer (maybe an overlay ? not sure
of the right technology or terminology there). The even frames
could be transferred to system memory, for recording to
disk. That particular option restricted recording and viewing
to 320x240. Or, you could record at 640x480, but not preview
at the same time. So, there was some flexibility there, but
due to the uncompressed data formats, a significant chunk of
bus bandwidth gets used by those old technologies. If the
PCI Express bus interface was used with chips like that now,
it would be much less of an issue.

PDF page 58 of this BT878 datasheet, shows just how flexible the
DMA engine is in this chip. This will give you some idea how
that generation of tuner products did it.

http://web.archive.org/web/20021204...rvlets/DownloadServlet/100119a.pdf?FileId=542

Paul

 

[David Maynard]

I'm wondering if a TV tuner with VGA on the same board (like ATI
All-in-Wonder) doesn't use the PCI bus to get the data to the monitor.

Correct. Which means you can not do any real time processing, like noise
filtering, judder elimination, etc., of the video signal. It goes direct to
the monitor just like it came in.

Would I be right to assume that separate tuner boards can't use bus
mastering to get the picture directly to the video card, and the video data
has to be processed by the CPU first?

I don't know whether it "can't" as I use them to do processing and, so,
never looked into that.

 

[kony]

I'm wondering if a TV tuner with VGA on the same board (like ATI
All-in-Wonder) doesn't use the PCI bus to get the data to the monitor.

What makes you think it'd use the PCI bus?
What would be on the PCI bus that it's communicating with?
Nothing. At most, the audio is on the PCI bus, maybe HDDs
if you're capturing the video but even then, not with a
modern board using the southbridge (or one chip/chipset) for
it's integral drive controller.

Would I be right to assume that separate tuner boards can't use bus
mastering to get the picture directly to the video card,

No, where are you getting these ideas?
Bus mastering either is or isn't supported by the card's
bridge(ing) chip. On any/all modern so-called tuner boards,
which are actually video capture cards that just happen to
have a tuner on them, too, bus mastering is supported and
used.

and the video data
has to be processed by the CPU first?

No.
Video data goes straight to the video GPU as an overlay,
there is no processing of it first. The CPU will handle
general software that displays this image, as another
operating system application, but not the video data itself.

On the other hand, if you are actively capturing, without
hardward (or partial) assist in compression, then the CPU
does process, encode this video.

In some cases, your capture/tuner card might have a sort of
replay-feature, which means it is always encoding a certain
period of video to have it available for playback
*instantly*. That is a wasteful way to use CPU time, but
if the feature is important, that's the only way to do it
since we have no magic time machines to go back to when it
first played. If your software supports this, it should be
obvious enough as it is a prominent feature. If it is, you
may be able to disable it- I make no guess there as any
software is subject to the creator's desires.

The all-in-ones don't use any bus bandwidth for watching (not recording of
course), right?

"Bus" means what?
PCI? Not for the video data. If during your use you make
use of _another_ PCI device, there's traffic but it's not
inherant to only displaying the incoming capture/tuner feed
as an overlay, "watching" it. You may however have audio
going to a sound card (device) on the PCI bus, and it may
even use a minor amount of CPU time. It's not enough to get
excited about.

Perhaps a better direction here is to ask what importance
this information has, what is your goal and need?

Generally speaking, it is not a problem to use a PCI
capture/tuner card, one does not go with an all-integral
card for this reason alone, usually, and plenty of people
have separate PCI capture/tuner cards as they are the
majority of the products in the field.

I know the impact might be insignificant, but that's a separate question.
I still would like to understand how the things work, and how they use the
bus. Thanks.

The PCI bus is for devices _on_ it. AGP card is not on the
PCI bus.

 

[kony]

Correct. Which means you can not do any real time processing, like noise
filtering, judder elimination, etc., of the video signal. It goes direct to
the monitor just like it came in.

Well, you could if you really wanted to... take D-scaler for
example, it does, but then it's not a direct overlay anymore
then, AFAIK, but that doesn't necessarily mean it couldn't
create the overlay itself, just as other programs such as
Media Player(s) do.

 

[Tom Del Rosso]

As for your question about separate tuner boards, at least the
BT848/BT878 family had an option to DMA to two separate
memory areas. [snip]

Thanks for all that info. I didn't even know video boards could accept
data DMA'd into their buffers without conflicting with the video driver.
If they do it to the overlay buffer then it makes sense, although I wonder
if that could ever conflict, or if the tuner driver can tell the video
driver that the overlay buffer is not available for other purposes.

PDF page 58 of this BT878 datasheet, shows just how flexible the
DMA engine is in this chip. This will give you some idea how
that generation of tuner products did it.

http://web.archive.org/web/20021204...rvlets/DownloadServlet/100119a.pdf?FileId=542

Thanks. I take it this is not a member of the current generation of video
processors. Is there a current one that you would look for in a new board?

 

[Tom Del Rosso]

Correct. Which means you can not do any real time processing, like noise
filtering, judder elimination, etc., of the video signal. It goes direct to
the monitor just like it came in.

So the separate board is preferable then - the opposite of what I thought.
Thanks.

 

[David Maynard]

Well, you could if you really wanted to... take D-scaler for
example, it does,

Not with an AIW it doesn't. Don't work at all.

 

[kony]

Not with an AIW it doesn't. Don't work at all.

Yes but isn't that for an entirely different reason, that
ATI isn't forthcoming with details on their products?

 

[Tom Del Rosso]

What makes you think it'd use the PCI bus?
What would be on the PCI bus that it's communicating with?
Nothing. At most, the audio is on the PCI bus, maybe HDDs
if you're capturing the video but even then, not with a
modern board using the southbridge (or one chip/chipset) for
it's integral drive controller.

I'm asking. As you said in a reply to David Maynard, the data can be
processed by the CPU first. I asked if it must do so.

Although I should have said system bus there.

No, where are you getting these ideas?

They are questions, not ideas. We live in a world where the most popular
OS just recently became able to boot from removeable media. I'm skeptical
about the capabilities of products, that's all.

Even if you know something is so, you can still allow that there might be a
sensible reason to think otherwise. For a bus master to write to the video
card, I thought the video driver would have to know about it, and I didn't
think there was a mechanism for that. Now that I reconsider it, I suppose
the tuner driver could grab control of the buffer so the tuner hardware
could have access to it.

Bus mastering either is or isn't supported by the card's
bridge(ing) chip. On any/all modern so-called tuner boards,
which are actually video capture cards that just happen to
have a tuner on them, too, bus mastering is supported and
used.
Thanks.



No.
Video data goes straight to the video GPU as an overlay,
there is no processing of it first. The CPU will handle
general software that displays this image, as another
operating system application, but not the video data itself.

On the other hand, if you are actively capturing, without
hardward (or partial) assist in compression, then the CPU
does process, encode this video.

In some cases, your capture/tuner card might have a sort of
replay-feature, which means it is always encoding a certain
period of video to have it available for playback
*instantly*. That is a wasteful way to use CPU time, but
if the feature is important, that's the only way to do it
since we have no magic time machines to go back to when it
first played. If your software supports this, it should be
obvious enough as it is a prominent feature. If it is, you
may be able to disable it- I make no guess there as any
software is subject to the creator's desires.

Thanks again for elaborating.

"Bus" means what?
PCI?

Yes, but I had another question in mind that I didn't ask. What if the DMA
transfer is between a PCI tuner and a PCIe video card? Would that utilize
the local bus (with a new chipset)?

Not that it really matters I guess. PCI has a 30ns cycle time, but (if I
try to be optimistic now) presumably the chipset will not capture the local
bus for longer than necessary.

Not for the video data. If during your use you make
use of _another_ PCI device, there's traffic but it's not
inherant to only displaying the incoming capture/tuner feed
as an overlay, "watching" it. You may however have audio
going to a sound card (device) on the PCI bus, and it may
even use a minor amount of CPU time. It's not enough to get
excited about.

Perhaps a better direction here is to ask what importance
this information has, what is your goal and need?

Mainly I wanted to know if there was an advantage to getting an all-in-one
card. But generally I wanted more background info before I bought one.

Generally speaking, it is not a problem to use a PCI
capture/tuner card, one does not go with an all-integral
card for this reason alone, usually, and plenty of people
have separate PCI capture/tuner cards as they are the
majority of the products in the field.

I see that Hauppauge is most popular but they make only tuner cards. Now I
don't have to consider the brands that make all-in-one cards.

The PCI bus is for devices _on_ it. AGP card is not on the
PCI bus.

I don't have AGP, but I do realize that if the transfer was just between
two PCI cards then it would be isolated by the southbridge.

 

[kony]

Yes, but I had another question in mind that I didn't ask. What if the DMA
transfer is between a PCI tuner and a PCIe video card? Would that utilize
the local bus (with a new chipset)?

yes, the data must travel "a" bus to get from one device to
memory to another device.

Not that it really matters I guess. PCI has a 30ns cycle time, but (if I
try to be optimistic now) presumably the chipset will not capture the local
bus for longer than necessary.

Optimistic of what?
That it works? Is that not obvious by products existing?

I can't give you a bus utilization figure because I simply
don't know that, but unless you have an expectation of a lot
of simultaneous PCI traffic, what would the gain be to
having an empty bus, or lower utilization?

Mainly I wanted to know if there was an advantage to getting an all-in-one
card. But generally I wanted more background info before I bought one.

The most significant features can vary per user.

Some of the things I would consider most;

Does it allow all the popular codecs for compression or just
whatever the software creator allows?

Is the remote control nicely designed.

Is the software interface nicely designed, and yet, not
overly wasteful of screen real-estate.

Does it work properly (sadly enough, random bugs are common
and even worse, random means your luck may differ from
others'). Two people can seeminly set up the same card and
software only to find that one can't schedule a recording
and have it reliably (start) recording. Perhaps they killed
the loader, perhaps they stopped some OS process, there's
not enough information shared about specific environments to
always know the status of software until you actually try it
yourself.

Cost - Do they cripple a card and require paying a lot more
for some basic features (like hardware compression, IF you
want that).

Timely software updates - as written above, bugs are common
and resolution will naturally require newer software or
driver or both.

Large user base- curious users with a little background in
tnuer/capture cards are often far more useful than tech
support from the company that made the product.

Digital tuner - generally better picture, appears to be
higher SNR but if your incoming signal is good quality it
may not matter as much.

I"m sure there are a lot more features that just don't come
to mind at the moment, or perhaps some things I just take
for granted, there are a lot of cards out there...

I see that Hauppauge is most popular but they make only tuner cards. Now I
don't have to consider the brands that make all-in-one cards.

True, but that doesn't necessarily rule them out either if
you needed a video card upgrade as well... but then if
you're the type of person to often upgrade the video card,
again it makes less sense to pay a premium over and over for
the tuner/capture functionality rather than having it in a
separate card.

 

[J. Clarke]

Not with an AIW it doesn't. Don't work at all.

Well, of course it doesn't. The AIW has an ATI Rage Theatre chip, not a
Conexant or Phillips or Brooktree. dScaler doesn't support the Rage
Theatre mainly because ATI has made it almost impossible for a third party
developer to get access to the specifications needed to support it.

It's not a matter of the chip being on the video board--the same difficulty
arises if they are on separate boards--dScaler doesn't work with the TV
Wonder Elite either for the same reason.