Legacy AV In for OSSC Pro

[Hojo_Norem]

Just discovered that this was up in the shop (out of stock atm) and I have a few questions:

One, I don’t really have the room for the module to stick out the side of the main unit.  I’m thinking on making a short riser board to mount the module above the main unit inverted and facing inward of the main unit.  This would add about 4 to 5 cm to the signal traces.  Would the extra length impact the signal integrity significantly?

Two, going by the image in the newsletter, is the orientation of the RF input final?  Is there a specific reason it isn’t facing the same direction as the composite and S-Video inputs?

And three, is there a footprint compatible ‘Belling-Lee’ type RF connector that I could replace the F-type with, rather than having to resort to adapters?

Thanks.

[marqs]

Minor signal trace length addition should not matter for this expansion as its bandwidth is low.

The photo is from first prototype where factory installed RF connector 90 deg wrong. The current production unit has RF related parts stripped out since FW support has not been done yet.

Suitable RF connectors are more or less a rarity these days. I could only find that one from large distributors (Digikey, Mouser etc.).

[Hojo_Norem]

Thanks. The price is at that point that I won’t mind putting a soldering iron to it to fit a local RF connector.
Do you have the rough dimensions of the module pcb? I might try to hunt down a suitable enclosure.

[ickwit]

Just an update that RF support is now live in the Firmware (as of 3 weeks ago).  Can’t wait until their old stock runs out so they can start building the updated RF version!

• This reply was modified 2 months, 2 weeks ago by ickwit.

[Hojo_Norem]

Just noticed that the non-RF version has just gone out of stock.  If the next batch is going to the RF model then I’m still down for one.

On a related note, does the decoding IC properly implement the delay line part of PAL decoding or is it something that is/will need to be simulated on the FPGA?

[marqs]

The RF-enabled board is still under development. The latest prototype due in 1-2 weeks should be final assuming it resolves the remaining noise coupling issues.

Composite decoding (from RF and CBVS RCA inputs) is done via ADV7280A which includes 2D comb filter and delay/storage circuits related to it.

[Hojo_Norem]

Nice.  I look forward to it.

[belaku]

Hello.

I am using Legacy AV Input and connecting a Japanese New Famicom (NES) to
OSSC Pro via Composite Video.

The modes are as follows:

LM Adaptive
Output 720p
Firmware version 0.78

When I connect the HDMI cable to the TV,
the screen is displayed in wide size 16:9, which is a problem.
How can I display the screen in normal size 4:3?

[marqs]

Try using scaler mode instead since it’s not possible to control sampling rate for cvbs/s-video decoder chip which would be needed for accurate aspect in LM modes. Alternatively you can select A-LM 1080p output which should result to aspect which is at least closer to 4:3.

[belaku]

Thank you for your reply.

It’s true that the Scaler mode makes it 4:3,
but I would like to use the Adaptive LM or Pure LM mode,
which have less delay than the Scaler mode.
A-LM 1080p didn’t work on my TV.
Will it be possible to make 4:3 and 16:9 selectable in a future firmware update?

[Zacabeb]

The dilemma is that the output from the ADV7280 that does decoding of composite and S-video in the Legacy AV Adapter is always rescaled internally in that IC to a 720 sample wide output.

Even if that’s then trimmed down to only the width of the actual graphics, for instance 640 samples, those will have to be either fit to a single pixel in the 1280×720 output or doubled to fill it. Either way the picture gets the wrong aspect ratio.

A solution to avoid the delay from Scaler mode would be to implement a horizontal-only polyphase scaling function also in A-LM mode so the picture can get scaled to an arbitrary width.

The challenge with that, I imagine, is getting the scaler IP core from Intel/Altera that’s used to accept reading from and writing to a small buffer of only a few lines rather than a full frame buffer as it does normally.

[belaku]

Thank you for your explanation.
Hmm…
So it’s a difficult problem.
For example, is it possible to make a “Legacy AV Input” specifically for 4:3 normal?
If that’s not possible, I’ll give up.

Thank you in advance.

[marqs]

The premise in LM modes has been that they only apply integer multiplication in X and Y directions. That works fairly well for analog content where aspect adjustment can be made by controlling sampling, but has its limitations with digital sources and ADV7280 which has fixed samplerate. A simple nearest neighbor / linear horizontal resampler could be added for LM but I’m afraid the end result in many cases would not look good enough to justify the effort. Does 1080p work at all on your TV? With A-LM the signal should be spec-compliant aside from refresh rate which is set by the source.

[belaku]

Sorry, A-LM 1080p (Line4x) works on my TV.
The aspect ratio is 4:3 normal, which is great.
It was P-LM 1080p that didn’t work, I was mistaken.
Unfortunately, black bars appear at the top and bottom.
In 1080p (Line5x), the top and bottom go off the screen.
But I’m going to keep using this mode.

Thanks for your explanation.

[Author]

Posts