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 Post subject: Re: F8 fantasy console!
PostPosted: Sun Aug 05, 2018 11:32 pm 
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my 'it' was in reference to "a Fantasy Console", not their fantasy console.

And I forgot a couple of things that I forgot a NES doesn't natively have...

Raster Interrupts
Timers
Fast mul/div registers

And stuff nothing has
FIFO hardware stack registers

;)


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 2:08 am 
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It's always cool to invent machines that could have been there in the 80s.

Personally, if I had a fantasy console to make I'd make it store games on VHS tapes, and use them for CGI too, just like later CD-based consoles used CD for both storing the game and the music. Of course by todays standards it'd be shitty, but back then this would have made a CDi like-console, a great platform for shitty games. Or I'd use casettes for both game data and music, that'd be fun too.

Sharing RAM and VRAM among the same adress spaces simplifies programming, but it means halving the bandwith, so halving CPU processing power and PPU limiting graphics (for example in the C64 if you want colours, each pixels is repeated twice horizontally because of that). You could just say "well let's double the clock speed then", but then you have to have expensive fast RAM in each console shipped, and expensive fast ROMs in game cartridges (if that support is used). If insteads games are loaded from some magnetic support in RAM, then you need even more expensive RAM in the console.


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 3:46 am 
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Quote:
Mhm. The priority bit determines if it's drawn in front of or behind the background. 1 is behind, 0 is in front.


https://wiki.nesdev.com/w/index.php/Fil ... _quirk.png

rainwarrior mentioned it already, but here's a visualization from the nesdev wiki. This case was of course unintentional, but some of the utility of the effect is that it requires 0 cycles to mask sprites this way since it is hardware accelerated (virtual hardware in this case of course). If a system allows for more (all?) sprites to be shown on the same scanline, its utility would be maximized.

full article:
https://wiki.nesdev.com/w/index.php/PPU_sprite_priority

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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 9:22 am 
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I'd say if you want a fantasy 8-bit console as a step up from the NES or the SMS, you could do a lot worse than a TurboGrafx-16.

  • 7.16 MHz 65C02 CPU core, faster in some ways than even the Blast Processing of a Genesis
  • Read and write video memory at any time using fast multi-byte copy instructions (similar to DMA)
  • Pixel clock switchable between 5.37 MHz with 256x224 pixels and 7.16 MHz with 336x224 pixels. Ideal for supporting both 4:3 and 16:9 TVs with the same assets designed for 8:7 PAR.
  • 16-pixel-wide sprites, 16 per line, for up to 75% coverage in widescreen
  • Tiles have 4 bits per pixel
  • Each 8x8 pixel background tile has one of 16 different 15-color background palettes, and each 8x8 pixel background tile has one of 16 different 15-color background palettes
  • Palettes have 3 bits per channel, like the Genesis without its shadow/highlight modes
  • Only one background layer (without the rare, Japan-only SuperGrafx revision) but the fast CPU and VRAM interface allows for practical generation of repeating background patterns in software (like Battletoads for NES and Prehistorik Man for Game Boy)
  • Wavetable audio similar to Konami SCC, Namco 163, or Virtual Boy


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 11:25 am 
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Bregalad wrote:
Sharing RAM and VRAM among the same adress spaces simplifies programming, but it means halving the bandwith, so halving CPU processing power and PPU limiting graphics (for example in the C64 if you want colours, each pixels is repeated twice horizontally because of that). You could just say "well let's double the clock speed then", but then you have to have expensive fast RAM in each console shipped, and expensive fast ROMs in game cartridges (if that support is used). If insteads games are loaded from some magnetic support in RAM, then you need even more expensive RAM in the console.

There's no capability of raster synchronization in this design, so the specific timings of things don't seem to be important for this system*. Suspending the CPU at NMI to draw everything at once to a framebuffer is an option, they don't necessarily have to use the CPU bus in tandem. ...not that this would have worked for the NES, but it's probably how this thing is already implemented in effect anyway? On modern systems the GPU waits for the frame to finish drawing before displaying, that's a very natural paradigm once you have the buffer. At its minimum RAM requirement maybe NMI could just be a block transfer of ~16k of render data for the frame to the "PPU".

* I think even the audio channels lack phase reset, so even the potential for 4-bit PCM is stifled.


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 11:27 am 
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After looking at my existing specs, I realized that I have enough RAM to give each 8x8 tile its own palette, and double the size of OAM (though the latter would require I move the palette data back a bit to make OAM contiguous). I will make these changes, and double the clock speed to 65536 cycles per frame.

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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:12 pm 
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I'm still not clear on how 256x192 with square pixels is possible without wide black borders on all sides. Is this not an NTSC console?


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:17 pm 
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93143 wrote:
I'm still not clear on how 256x192 with square pixels is possible without wide black borders on all sides. Is this not an NTSC console?

It's not NTSC, it runs on a PC.

That is a valid issue though, I guess you'd have to implement some 4:5 vertical scaling if your really wanted it to run on an NTSC TV.


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:22 pm 
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rainwarrior wrote:
Bregalad wrote:
Sharing RAM and VRAM among the same adress spaces simplifies programming, but it means halving the bandwith, so halving CPU processing power and PPU limiting graphics (for example in the C64 if you want colours, each pixels is repeated twice horizontally because of that). You could just say "well let's double the clock speed then", but then you have to have expensive fast RAM in each console shipped, and expensive fast ROMs in game cartridges (if that support is used). If insteads games are loaded from some magnetic support in RAM, then you need even more expensive RAM in the console.

There's no capability of raster synchronization in this design, so the specific timings of things don't seem to be important for this system*. Suspending the CPU at NMI to draw everything at once to a framebuffer is an option, they don't necessarily have to use the CPU bus in tandem. ...not that this would have worked for the NES, but it's probably how this thing is already implemented in effect anyway? On modern systems the GPU waits for the frame to finish drawing before displaying, that's a very natural paradigm once you have the buffer. At its minimum RAM requirement maybe NMI could just be a block transfer of ~16k of render data for the frame to the "PPU".

* I think even the audio channels lack phase reset, so even the potential for 4-bit PCM is stifled.

As for when the framebuffer is drawn, it's drawn all at once, so you can write to "PPU" memory any time. A hardware version would just copy $4000-$7FFF to a local cache and then draw that.

As for phase reset, not sure what that is.

93143 wrote:
I'm still not clear on how 256x192 with square pixels is possible without wide black borders on all sides. Is this not an NTSC console?

I thought SDTV NTSC was 4:3
https://en.wikipedia.org/wiki/480i

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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:41 pm 
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Fautenic wrote:
[As for phase reset, not sure what that is.

It's being able to reset an oscillator to the beginning of its cycle. If the square signal started high, then goes low in the second half of the cycle, you could set the frequency low and keep resetting the phase to keep it always high. That'd make 4-bit CPU-driven PCM possible, but only if the CPU is uninterrupted across the frames. (The graphics buffering scheme would probably make that impossible.)

Fautenic wrote:
93143 wrote:
I'm still not clear on how 256x192 with square pixels is possible without wide black borders on all sides. Is this not an NTSC console?

I thought SDTV NTSC was 4:3
https://en.wikipedia.org/wiki/480i

That number "480" is important. NTSC does not have a variable number of lines. (The horizontal resolution can be varied a lot, however, as it's just an analogue signal anyway.)

You have 192 lines. Either you have 48 blank lines to fill out the rest of a 240p picture, or you have to do a vertical rescaling.


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:42 pm 
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The glass is 4:3 (Or at least, has been since ... uh, late 1960s?)

Old glass CRTs didn't have a fixed number of pixels. By changing the specific rate at which a digital device emits pixels, the width of each pixel changes accordingly.

So the specific amount of image that's encoded in the signal (e.g. 640x480i that's overscanned so only ≈600x448 is visible) means that a 256x192 console with square pixels would be "windowboxed" like the C64.

Consoles like the Master System that drew 192-scanline-high video modes instead often stretched the pixels a little bit horizontally to make the display more nearly full-width; correspondingly the screen is letterboxed.


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 1:54 pm 
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lidnariq wrote:
Consoles like the Master System that drew 192-scanline-high video modes instead often stretched the pixels a little bit horizontally to make the display more nearly full-width; correspondingly the screen is letterboxed.

I'd forgotten that the SMS did that!

Thinking more about the actual dimensions represented here, the letterboxing doesn't seem that bad... 24 lines at the top and bottom, partially cropped anyway so it's more like 16 visible blanks? The corresponding pillarboxes would be a little more prominent, but maybe not a huge problem. Also eliminates the "safe area" problem that we normally have with TVs.

Then again I grew up with an Atari ST which had a big empty colour-0 border around the screen at all times...


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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 5:21 pm 
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Updated the console, now it has a palette entry for each 8x8 tile, twice as much OAM, and twice the clock speed.

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 Post subject: Re: F8 fantasy console!
PostPosted: Mon Aug 06, 2018 5:22 pm 
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Send 240p pixels at 3.5 NES master clocks (7 edges) per pixel, and they'll be square. A 256x192 pixel screen at this dot clock rate will be exactly as big as 224x192 pixels on a ColecoVision, NES, or SMS, which is also conveniently the size of the 80% title safe area marked on Nintendo's background planning sheet. So yes, it'd be underscanned like a 1980s home computer.


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 Post subject: Re: F8 fantasy console!
PostPosted: Tue Aug 07, 2018 9:25 am 
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Two more questions for you all:

Anyone at all interested in development for this console? Would porting to/from NES as far as homebrew is concerned be doable?
How commercially viable would a game built for this console be (something like Shovel Knight comes to mind)?

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