Video output considerations

Open source STF clone project.
Petari
Posts: 193
Joined: Tue Nov 28, 2017 1:32 pm

Re: Video output considerations

Post by Petari » Wed Jan 03, 2018 8:22 am

exxos wrote:
Tue Jan 02, 2018 10:39 pm
Probably one method is to copy the video data from shifter (binary outputs) and use a PLD (assuming enough RAM) for frame buffer. Then the frame/ram buffer would be dual channel, so any refresh rate could be used, and is read from the buffer. Buffer could output at 100hz then for example.
Yep. that's my concept. But it needs about 1MB very fast RAM, to work well. For instance, 100 Hz output may need very high freq. pixel clockrate. And during it, RAM must be accessible for writing from ST side. SRAM is very expensive. So, probably should go on SDRAM, but it needs more complex control. 100 Hz sounds great, but what monitors can do it ?
Maybe 75 Hz is what should target - that works on most of cheaper monitors, in little lower resolutions.
Just tested Steem in fullscreen mode, refresh rate set to 75 Hz, at res 640x480, 50 fps game (Sideways), and it was perfect - no tearing (when V-sync on), no visible judder. 75 Hz is max what my monitor can, and I think that it is same with majority.

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IngoQ
Posts: 491
Joined: Tue Aug 22, 2017 8:38 am
Location: Germany

Re: Video output considerations

Post by IngoQ » Wed Jan 03, 2018 9:34 am

Wouldn't it be easier to offload all this to a dedicated video chip?

Chrontel seems to have a nice lineage, the CH70300 sounds like beeing up for the job:
  • DVI encoder support up to 1080p
  • Supports Component YPrPb (HDTV) up to 1080p and analog RGB (VGA) monitor up to 1920x1080 resolution
  • Hot plug detection for DVI
  • TV/Monitor connection detect capability. DACs can be switched off through programming internal registers
  • Pixel-level color enhancement for brightness, contrast, hue and saturation adjustment for HDTV and VGA output
  • On-chip frame buffer supports frame rate conversion provides the graphic controller the flexibility of video timing output
  • Advanced scaling engine to upsize/downsize input resolution for DVI display up to 1080p, VGA up to 1920 x1080 and HDTV up to 1080p
  • Supports 8/12/16/18/24-bit parallel interface input for either RGB format (RGB-565, RGB-666 or RGB-888 and etc.) or YCrCb format (ITU-R 656 or ITU-R 601). 80/86 MPU interface and DE only mode are also supported.
  • Image display rotation support at 90/180/270 degree or flipped in horizontal/vertical position
  • IO Supply Voltages from 1.2V to 3.3V and SPC/SPD Supply Voltages from 1.8V to 3.3V.
  • Programmable power management
  • Device fully programmable through serial port or can automatically load firmware from Chrontel Boot ROM (CH9904)
  • Offered in a 88-pin QFN package
See here for more details:

http://www.chrontel.com/product/detail/54#
Ingo :geek:

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.” - Antoine de Saint-Exupéry

Petari
Posts: 193
Joined: Tue Nov 28, 2017 1:32 pm

Re: Video output considerations

Post by Petari » Wed Jan 03, 2018 1:23 pm

IngoQ wrote:
Wed Jan 03, 2018 9:34 am
Wouldn't it be easier to offload all this to a dedicated video chip?
http://www.chrontel.com/product/detail/54#
Certainly would be easier. And even more easy would be usage of mentioned Philips TV :D
But then, where is the fun, where is learning of some things ? As usual, it can be solved in many ways, we need to consider all realistic, not expensive ways available.
In any case, it seems as something what can do the job well,for decent price - about 20 Euros. I think that for PAL source 75 Hz rate would be best, and it works on most LCD monitors at lower resolutions, and we don't need 1080p for Atari .

Petari
Posts: 193
Joined: Tue Nov 28, 2017 1:32 pm

Re: Video output considerations

Post by Petari » Thu Jan 04, 2018 10:12 am

Looked little more that Chrontel CH7033 (not 70300) .
It seems that it has all we need. Separated clock input for source video, framerate conversion, analog + DVI output, so probably good for HDMI too.
But to make it work, you need to program it - or in other words - to set it in desired mode, what means setting output freq., resolution and other things.
That goes via serial port - so there is need to add extra serial port, where can set somehow working modes. And it needs, if I see it right boot ROM attached - CH9904 . I can't find it's price, but is low for sure - it is just serial EPROM, if I see it right.

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