HoboHaxor
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Secondary disply (AV/Composite)

Mon Jan 28, 2019 7:40 pm

I have a few of the El Cheapo back up camera displays and wondering if there are any HATs/PHATs that would allow me to display other *secondary* info via composite AV; NOT mirror the HDMI.
My use case is data/graphs. Won't need fast refresh.

(Yes, I know all about the built in composite port/pins, but that just mirrors, as best it can, the HDMI)

jamesh
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Re: Secondary disply (AV/Composite)

Mon Jan 28, 2019 9:01 pm

The multiple frame buffer code will, I think, allow different data on composite. although I don't think I tried that combination.

See the thread on how to try it out. Still in beta.

viewtopic.php?t=216399&start=150
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6by9
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Re: Secondary disply (AV/Composite)

Tue Jan 29, 2019 6:51 am

Iirc The composite and hdmi outputs are mutually exclusive within the SoC.

You could use the dpi interface to produce rgb at standard sd rates, and then a pal encoder to convert to composite. Dpi and hdmi/composite are possible simultaneously. I'm not aware of any hats that do that though, but it's only a variation on the vga666 board.
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jamesh
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Re: Secondary disply (AV/Composite)

Tue Jan 29, 2019 10:05 am

6by9 wrote:
Tue Jan 29, 2019 6:51 am
Iirc The composite and hdmi outputs are mutually exclusive within the SoC.

You could use the dpi interface to produce rgb at standard sd rates, and then a pal encoder to convert to composite. Dpi and hdmi/composite are possible simultaneously. I'm not aware of any hats that do that though, but it's only a variation on the vga666 board.
Now that i think about it, ISTR something along those lines. Same pixel valve? Anyway, probably cannot have composite and HDMI working at the same time. Shame.
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6by9
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Re: Secondary disply (AV/Composite)

Tue Jan 29, 2019 10:39 am

jamesh wrote:
Tue Jan 29, 2019 10:05 am
6by9 wrote:
Tue Jan 29, 2019 6:51 am
Iirc The composite and hdmi outputs are mutually exclusive within the SoC.

You could use the dpi interface to produce rgb at standard sd rates, and then a pal encoder to convert to composite. Dpi and hdmi/composite are possible simultaneously. I'm not aware of any hats that do that though, but it's only a variation on the vga666 board.
Now that i think about it, ISTR something along those lines. Same pixel valve? Anyway, probably cannot have composite and HDMI working at the same time. Shame.
https://github.com/raspberrypi/firmware ... -455556619
Both use pixelvalve 2.
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aBUGSworstnightmare
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Re: Secondary disply (AV/Composite)

Tue Jan 29, 2019 4:29 pm

Might be same 'cause' as with DSI + DPI, which is also impossible.

Do you know the display part number (module name)? If it's RGB you can connect it to DPI. You will have to design/build the HAT yourself (but it's not rocket science)

6by9
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Re: Secondary disply (AV/Composite)

Tue Jan 29, 2019 5:11 pm

aBUGSworstnightmare wrote:
Tue Jan 29, 2019 4:29 pm
Might be same 'cause' as with DSI + DPI, which is also impossible.
From the docs, DPI+DSI1+HDMI is possible. Getting the correct range of settings is a different matter.
The main reason that it is impossible at the moment is that the code currently reads

Code: Select all

   if (enable_dpi_lcd)
   {
      // Default to HDMI with VGA / DPI unless config.txt overrides
      <INIT DPI>
   }
   else if (!ignore_lcd)
   {
     <INIT DSI>
   }
   <INIT HDMI>
   <INIT COMPOSITE>
I don't believe James changed that bit with his multiple frame buffer stuff, therefore only one or other gets initialised.
It's the same lump of code that needs refactoring if we want to support 2 DSI displays on the CM.

It gets more confusing with how DispmanX identifies the screens, which is the default, and trying to maintain backwards compatibility.
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