AM68A: DSS configuration for Bt656 interlaced output

Frank,

Frame blanking is used for progressive output and Field blanking is for interlaced output. 

Regards,

Brijesh

Both descriptions appear under interlaced mode/output! I guess you wrote the FAQ (your name appear above it) and in this FAQ we find the "vertical frame blanking" under "interlaced output format".

But that's not the point we are interested in. We are more interested in the numbers. In one description the front porch stands for '2' in the other for '1'. So please can someone explain the meaning of '1' and '2' in the description of the values?

Frank

Frank Bergmann said:

Both descriptions appear under interlaced mode/output! I guess you wrote the FAQ (your name appear above it) and in this FAQ we find the "vertical frame blanking" under "interlaced output format".

ok, please use field blanking for interlaced mode. 

Frank Bergmann said:

But that's not the point we are interested in. We are more interested in the numbers. In one description the front porch stands for '2' in the other for '1'. So please can someone explain the meaning of '1' and '2' in the description of the values?

Sorry, where do you see/get 1 or 2 values for the front porch? Is it from some datasheet? 

Regards,

Brijesh

In your FAQ you wrote for example: "vBackPorch: This parameter is used to specify vertical frame blanking-1 for the odd field". In this quote you find the number "1".

And the reference manual (SPRUJ28E, page 1699) states: "Vertical field blanking No.2 for Odd Field is set in the DSS0_VP_TIMING_V[31-20] VBP bit field." Here we can read blanking no 2.

These are the numbers we are interested in!

Frank

Please refer to reference manual in this case.. 

Regards,

Brijesh 

Brijesh Jadav said:

Please refer to reference manual in this case.. 

So it means your FAQ is not correct?

The reference manual does not explain "Vertical field blanking No.1" and "Vertical field blanking No.2". What does these values describe?

Frank

FAQ has typos.. 

Please refer to BT656 specs to understand different blanking parameters. 

Regards,

Brijesh

When we look into the Bt656 specification we can't find "Vertical field blanking No.1".

Can someone please explain the mapping of TI's description to the parameters in the Bt656 specification?

Frank

Please check this image and figure out blanking regions. blanking-1 is typically at the top of the frame and blanking-2 at the bottom. 

Regards,

Brijesh

Do you refer to the image I posted?

What means "typically"? It sound like "not always, it depends...". Is it or is it not? Shall I experiment? Do behave every processor different? Or every processor boot? Please explain.

Frank

I am working on a similar problem related to BT656 and I think I know what those blanking intervals mean.

field blanking no1 is the blanking interval before the active video

field blanking no 2 is the blanking interval after the active video.

Consider the even field as follows:

vertical field blanking no 1 for odd field -> vertical field blanking no 2 for even field -> active video lines for even till the end of the field

and the odd field as follows

vertical field blanking no 1 for even field -> vertical field blanking no 2 for odd field -> active video lines for odd till the end of the field

So the no 2 field actually occupies the start of the next field.

This is what I have figured out till now. If someone knows I am wrong, please correct me.

Regards,
Nikolay Nikolov

Nikolay, thanks for your answer!

Is your statement "field blanking no1" in terms of the processor reference manual or the FAQ for configuration of DSS for Bt656 I linked to above?

So for an example referring to NTSC:

vertical field blanking 2 for even (register: horizontal back porch) = 1

vertical field blanking 1 for odd (register: vertical front porch) = 20

vertical field blanking 2 for odd (register: vertical back porch) = 264

vertical field blanking 1 for even (register: horizontal front porch) = 283

Sounds this correct?

Nikolay Nikolov said:

This is what I have figured out till now. If someone knows I am wrong, please correct me.

It's sad that users has to figure it out. TI should know what is happen in their processors and describe it accordingly in the manuals.

Best regards,

Frank

Thanks for making me to double check what I have written. I corrected my post. I just changed the numbers of the fields.

And yes, these are the fields which you have mentioned - front and back porches in the non bt656 mode. In the bt656 mode they are vertical field blankings.

So consider first 19 lines of the even field as sum of vertical field blanking no 1 for odd field + vertical field blanking no 2 for even field

and first 19 lines of the odd field sumo of vertical field blanking no 1 for even field + vertical field blanking no 2 for odd field.

And do not forget odd field is one line less.

Regards,
Nikolay Nikolov

Thanks again Nikolay for your answer but sorry, maybe it's because friday, I'm more confused.

If I look into the Bt656 specification:

I can see 4 values specifying the vertical blanking. For NTSC (525 lines, right column) these are: (Line) 1, (Line) 20, (Line) 264 & (Line) 283. And these 4 values should be used (as I understand it correctly) for configuring the vertical blanking parameters:

(image taken from SPRUJ28E, page 1699)

I need the information how does the values from the Bt656 specification match to the blanking parameter in the reference manual of the processor.

With regards,

Frank

I understand it like this:

1. line 1 to line 20 - vertical field blanking for even field
2. line 264 to line 283 vertical field blanking for odd field

Other lines are active video with horizontal blanking at the end.

the vertical field blanking for even field consists of vertical field blanking no 1 for odd field + vertical field blanking no 2 for even field according to TI implementation. 

the vertical field blanking for odd field consists of vertical field blanking no 1 for even field + vertical field blanking no 2 for odd field field according to TI implementation.

I am not sure which standard these 4 blanking periods are compatible with. I do not know how to explain it better.

Regards,
Nikolay

Hi Nikolay,

you mentioned "according to TI implementation". Do you have a reference to this implementation?

[SPRUJ28E, page 1698]

In interlaced mode there two of this "fields" form one frame. It makes sense to label it vertical even No.1 (VFP) and No.2 (VBP).

With all required entries for interlaced mode (NTSC) is this equation fulfilled? (Even and odd field plus vblankings for both)

LPP + (LPP + DELTA_LPP) + (VBP'No1 + VFP'No1) + (VBP'No2 + VFP'No2) == 525 lines

And for the horizontal blanking, the blue active video region is 'shifted' to the edge, and therefore:

PPL + "12 Bit value" == Total Line Length?

Many thanks for your support in advance

Martin

(Sorry for being late with my answer.)

Thank you very much!

The patch set found under the link explained a lot of the settings. With it I have a working Bt656 mode NTSC & PAL image.

Nikolay Nikolov said:

243 + (243+1) + 19 + 19 = 525

This doesn't work correctly for me better is:

(244 - 1) + 244 + 19 + 19 = 525 (using -1 for DELTA_LPP)

So the description in the Technical Reference Manual (SPRUJ28E, page 1699) seems to be misleading. One vertical field blanking is set with DSS0_VP_TIMING.HFP & DSS0_VP_TIMING_H.VFP and the one for the other field with DSS0_VP_TIMING_H.HBP & DSS0_VP_TIMING_V.VBP. The values HFP & HBP set the start (line) (which can be 0). VFP & VBP set the end or (?) length of the blanking. For NTSC these are 19 for both and 24/25 for PAL.

Best regards,

Frank

Hi Frank,

It is good to hear that your problem is solved.

I have put my reworked patches in that thread which should make things even more clear. But DELTA_LPP is fixed for my case there. I cannot think of a way to make it configurable for the moment. 

About HFP, HBP, VFP and VBP looks like in BT656 things are slightly different. There are no front and back porches but lets say front and back vertical blanking periods, before and after the active video. As active video is present till the last line of the frame the vertical blanking that must follow occupies the first lines of the next frame. At least this is how I understand it.

Regards,
Nikolay

Hi,

you could check against both vblank widths and decide the value for DELTA_LPP

DELTA_LPP = ((vblank1_width + vblank2_width) % 2) - 1

give you 0 if addition of both is odd and -1 if even. This should work for at least NTSC and PAL.

If you use (from your description) "243 + (243 + 1) ..." then your framebuffer has the size of 2 * 243 but one filed will show 244 lines. Where does the information for this line comes from?

Did you forget the colorspace conversion in you updated patch set?

With regards,

Frank

I have a check if DELTA_LPP has to be set to something:

(mode->vdisplay & 0x01) == 0x01

which means number of vertical lines is an odd value and DELTA_LPP must be set to something different than 0

The problem is it must be set to 1 or 2 but as the virtual blank intervals in bt656 are the same (19 lines) I cannot use these values to determine the DELTA_LPP. I put value 2 as bottom field in our case should be 1 line less. I do not know why it is different in your case. At least for BT656 it should be 2, this is how I understand it.
I still struggle to figure out how to configure this value according to some setting.

Could you explain why in your case is the opposite ?

Regards,
Nikolay