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PostPosted: Fri Oct 28, 2016 5:58 am 
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Location: Nacogdoches, Texas
Would it really be that expensive? I've found 8 bit shift registers for less than a dollar, although I'm assuming that they're not even a fraction as fast. I can't imagine the price being higher than $10, although you'll need 3 of them.


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PostPosted: Fri Oct 28, 2016 11:28 am 
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LOL PI ZERO
That's the eternal problem with rigging up ancient-style hardware, you get beaten by cheap new components.

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PostPosted: Fri Oct 28, 2016 11:41 am 
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Location: NE Indiana, USA (NTSC)
Granted. But how easily do "cheap new components" compete latency-wise with good old SPI bit banging for the input and scanline rendering for the video output? The average video latency on an NES or Super NES with wired controllers and a CRT SDTV is 2 frames or 33 ms:

  • Average 1/2 frame between button press and next controller read
  • Fixed 1 frame to process game logic, create a display list, and send it to the PPU
  • Average 1/2 frame from top of picture to player character's position

Kev's Hi-Def NES adds 1 to 2 ms at the most, plus whatever lag the TV's scaler adds.

How close do frame buffer based systems come?


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PostPosted: Fri Oct 28, 2016 12:27 pm 
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Location: Seattle
The cheapest digital-parallel-24-bit-to-HDMI IC seems to be the TDA19988 , at $5/@1 via Mouser. I think the biggest problem you'll have is that if you're using the "480i over HDMI" timing, the TV is going to deinterlace it, which will add tons of latency.

It wouldn't be hard to generate 640x480 at 1bpp—after all, the original VGA card managed 640x480@4bpp by using a 32-bit wide data bus and a 3MHz master clock—but it would get fiddly, and be more expensive than just using a cheap FPGA.


I suppose the question is, for anyone who has a linux machine and a Real TV, what happens if you try any of the following modelines?
Code:
xrandr --newmode "320x240in640x480-60" 25.175 320 656 752 800 240 490 492 525 -hsync -vsync; xrandr --addmode HDMI-1 "320x240in640x480-60"
xrandr --newmode "320x240in1280x240-60" 25.175 320 1312 1504 1600 240 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "320x240in1280x240-60"
xrandr --newmode "1440x242-BT601-60" 27 1440 1456 1584 1716 242 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "1440x242-BT601-60"


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PostPosted: Fri Oct 28, 2016 7:46 pm 
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lidnariq wrote:
I suppose the question is, for anyone who has a linux machine and a Real TV, what happens if you try any of the following modelines?
Code:
xrandr --newmode "320x240in640x480-60" 25.175 320 656 752 800 240 490 492 525 -hsync -vsync; xrandr --addmode HDMI-1 "320x240in640x480-60"
xrandr --newmode "320x240in1280x240-60" 25.175 320 1312 1504 1600 240 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "320x240in1280x240-60"
xrandr --newmode "1440x242-BT601-60" 27 1440 1456 1584 1716 242 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "1440x242-BT601-60"

I get a black screen on the first two and a very narrow image for the third. I can stretch it to fill the screen (with significant overscan) by changing the aspect ratio, but the scaler looks awful as usual.


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PostPosted: Fri Oct 28, 2016 9:49 pm 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
Very narrow PAR (expected) or very narrow DAR?


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PostPosted: Sat Oct 29, 2016 5:39 am 
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1:1 PAR by default. I can get the expected 4:3 DAR and ~2:9 PAR by hitting the aspect button a few times though.


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PostPosted: Tue Nov 01, 2016 3:58 pm 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
After a little while of thinking on it, I'm curious what happens if you use the functioning modeline ("BT601") but increase the horizontal blanking a lot so that its normal 1:1 PAR produces a 4:3 or 16:9 DAR?

i.e. 27 WIDTH 1456 1584 1716 240 245 248 262 -hsync -vsync with WIDTH = 320 or 424


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PostPosted: Tue Nov 01, 2016 7:15 pm 
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Joined: Thu Aug 20, 2015 3:09 am
Posts: 305
Both of these give me a blank screen, and a "NO SIGNAL" message when I switch from another input to HDMI:
Code:
xrandr --newmode "TEST1" 27 320 1456 1584 1716 240 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "TEST1"
xrandr --newmode "TEST2" 27 424 1456 1584 1716 240 245 248 262 -hsync -vsync; xrandr --addmode HDMI-1 "TEST2"

Do modern TVs even care about blanking? I'm pretty sure they'd just dump the active pixels into a framebuffer by now.


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