-heisenberg-
Posts: 21
Joined: Mon Dec 17, 2012 7:12 am

Progressive Scan RCA Video?

Sun Dec 30, 2012 3:08 pm

I finally dug up my trusty old Commodore 1084 monitor and tested out the RCA video. Movies look good, but using it for text/GUI will give you a migraine headache as the video is interlaced and flickers like hell.

What I'm looking for is a way to switch the video to progressive. Using a 640x200 resolution, one could display 80 column video in a decent quality, like on the Amiga. I tried creating a modeline in /etc/fb.modes and using fbset, but it seems that all commands to change the video mode are ignored by the RPi hardware.

When issuing tvservice -s, it actually shows progressive on DVI and interlaced on RCA, so I'm guessing it would be simple to add an option to the config.txt to have half the vertical resolution and progressive scan. This would be really awesome especially for running emulators as it would give a video output almost identical to the original.
arm_freq=1100 / core_freq=500 / sdram_freq=450 / over_voltage=6

Twinkletoes
Posts: 210
Joined: Fri May 25, 2012 9:44 pm

Re: Progressive Scan RCA Video?

Sun Dec 30, 2012 3:16 pm

Composite video (on the RCA connector) is interlaced by definition. Your monitor is expecting an interlaced signal. Nothing you can do about that I'm afraid.

-heisenberg-
Posts: 21
Joined: Mon Dec 17, 2012 7:12 am

Re: Progressive Scan RCA Video?

Sun Dec 30, 2012 5:14 pm

Composite video (on the RCA connector) is interlaced by definition. Your monitor is expecting an interlaced signal. Nothing you can do about that I'm afraid.
Uh, no, wrong. Completely untrue. What are you talking about? Please refrain from posting in topics you clearly know nothing about. I'm looking to get a specific problem fixed and you're not helping by adding possible confusion.

If you want to educate yourself, here's a starting point:

https://en.wikipedia.org/wiki/Interlaced

Please, read at least the last paragraph.

Every game console and computer ever used progressive scan video. Interlaced video makes a computer all but unusable for its intended purpose.
arm_freq=1100 / core_freq=500 / sdram_freq=450 / over_voltage=6

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liz
Raspberry Pi Foundation Employee & Forum Moderator
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Re: Progressive Scan RCA Video?

Sun Dec 30, 2012 5:21 pm

-heisenberg- wrote:
Composite video (on the RCA connector) is interlaced by definition. Your monitor is expecting an interlaced signal. Nothing you can do about that I'm afraid.
Uh, no, wrong. Completely untrue. What are you talking about? Please refrain from posting in topics you clearly know nothing about. I'm looking to get a specific problem fixed and you're not helping by adding possible confusion.

If you want to educate yourself, here's a starting point:

SNIP.
Hi Heisenberg. We go to quite a lot of effort here to make sure conversation is friendly and civil; broadly speaking, if you wouldn't say something to someone in their kitchen, don't say it to them here. Please try to keep this a nice place for people to visit.
Director of Communications, Raspberry Pi

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Burngate
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Re: Progressive Scan RCA Video?

Sun Dec 30, 2012 6:11 pm

On old-fashioned CRT televisions and monitors designed around broadcast PAL or NTSC, the scanning circuitry didn't really care about interlace.

The horizontal scanning circuit needed the line sync signal to be around 15kHz, while the vertical scanning circuit needed the field sync signal to be around 50Hz or 60Hz.

If the field sync signal caused the vertical fly-back to start at the beginning of a line on one field but half way through the line on the other field (which meant an odd number of lines for the whole two-field frame) then you had interlace.
Each field had an extra ½ line.

If the field sync signal came at the same point on the line on each field, then you had progressive scan, with one field per frame. The number of lines per field (or frame) inevitably had to be 240 or 288, given the restrictions on line and field frequency (and fly-back blanking). No extra ½ line in each field

But that choice of having (or not) that ½ line is down to the generating hardware. As far as I know it's built in to the Pi's hardware, and not changable (though I'm sure someone at Broadcom can confirm or deny that)

starquake
Posts: 5
Joined: Wed Apr 16, 2014 8:34 pm

Re: Progressive Scan RCA Video?

Fri Nov 18, 2016 3:30 pm

I created an issue on the github repo for the Raspberry PI firmware: https://github.com/raspberrypi/firmware/issues/683

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RaTTuS
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Re: Progressive Scan RCA Video?

Fri Nov 18, 2016 4:21 pm

no need to bump this one also
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