Understanding the design of the the Super Nintendo video system
fabiensanglard.net
fabiensanglard.net
This was something that took a bit to figure out, but made so much sense to me after I had been playing around with trying to learn game programming when I was a kid.
CGA/EGA/VGA all had popular 320x200 modes.
The NES was 256x224, as was the SNES (although it did have higher resolution modes), and that was really a TV limitation.
Meanwhile, Pac-man was 288x224 in the arcade.
So none of the Pacman clones on the PC would ever look 'right', and even the Pacman games on the NES that were made by Namco didn't look right either. There were always hacks like giant characters because the tiles for the map were smaller, or you'd get a scrolling world (Gameboy, Tengen versions), other kinds of distortion, non-original maps...it was all just weird and frustrating when you're trying to play the 'arcade' game at home.
But after learning the details of the machines, how sprites worked (and then coming to the conclusion that they just didn't have any other choice), was such a huge 'a-ha!' moment for me. Let's not even get into the fact that pixels aren't square on those resolutions on the PC.
And then it became almost an instant reaction when I'd see a Pacman port or clone, and try to figure out what size the world was, what size the tiles were, what size the sprites were....
The SNES's vertical resolution was configurable to either 224 or 240 lines, as the article mentions. Most games stuck with 224, as the longer vertical blanking interval gives you more time to transfer graphics to the PPU.
Adding further complication, although most arcade cabinet games also used 15Khz CRTs similar to de-cased televisions, since all the cabinets were being assembled by the manufacturer using CRTs they specified, designers could take some liberties with varying the resolution, frame rate, scan lines and scanning frequency of the video signal generated by their game's hardware circuit board. Being analog devices, CRTs of this era were generally tolerant of such variations within specified ranges since they had to sync up with inputs from disparate over-the-air television channels, cable boxes, VCRs or even live cameras. This allowed arcade hardware designers to optimize their circuits either for slightly better resolution and frame rates or alternatively reduce them somewhat in cases where their hardware wasn't quite able to generate enough pixels in real-time. For example, the Mortal Kombat 1, 2 and 3 cabinets displayed video at 54 Hz (instead of NTSC-standard 59.94 Hz) enabling higher horizontal resolution. They could also optionally choose to use the entire overscan safe area for active game pixels since they knew the CRT's width and height adjustments could be dialed on the cabinet manufacturing line to ensure the entire active picture area was visible inside the bezels - whereas few consumer TVs exposed all of these adjustments externally to users.
All this subtle variation in classic arcade hardware makes clock-for-clock, line-for-line accurate emulation especially challenging. Fortunately, the emulation community has solved this thorny set of problems with a special version of MAME called GroovyMAME which is designed specifically to generate precisely accurate emulated output signals so these emulated classic arcade games can be perfectly displayed on analog CRTs. This requires using one of the many PC graphics cards with native analog RGB output, which was most graphics cards made up to 2015 - but sadly none since. GroovyMAME works with specially modified Windows graphics card drivers to generate correct signal ranges from the analog output hardware of most off-the-shelf, pre-2015 Radeon and NVidia cards - which are still widely available on eBay ($10-$50).
For arcade preservationists and retro gaming purists, the resulting output to a CRT is sublime perfection, identical to the original cabinet hardware circuit boards, many of which are now dead or dying. This enables creating an emulation arcade cabinet either using a period-correct CRT matching the traits of a certain series of original cabinets, or alternatively, using a special tri-sync or quad-sync analog RGB CRT which is able to display a wide variety of signals in the 15Khz, 25Khz, 31Khz and 38Khz ranges. This is what I have in my dedicated analog CRT cabinet and using GroovyMAME along with a 2015 Radeon GPU it can precisely emulate 99+% of raster CRT arcade cabinets released from 1975 up to the early 2000s accurately (and automatically) recreating hundreds of different native resolutions, frame rates, pixel aspect ratios and scanning frequencies on my cabinet's 25-inch CRT. For more info on GroovyMAME and accurate CRT emulation visit this forum: http://forum.arcadecontrols.com/index.php/board,52.0.html.
What is the future for RGB-output video cards looking like? Are there more specialised cards still in production?
And are these tri-/quad-sync analog CRTs still manufactured?
The feeling of CRTs and contemporaneous hardware provokes almost overwhelming nostalgia for me, and I feel like modern television hardware is only just beginning to catch up with respect to UI responsiveness and reliability, for instance changing channel & volume, and playback functions like pausing, fast-forwarding and rewinding videos.
Sadly, no graphics card manufacturer still makes cards with native analog RGB output and, AFAIK there haven't been any since ~2015. There may be cards which have analog output but it's not natively generated with variable analog timing (dot clocks etc). Instead it's created as a native digital signal and then converted to analog, at which point it's no better than adding an analog converter externally to an HDMI or Displayport output connector (this is pointless and not worth doing).
On the positive side, there are a ton of used graphics cards with native analog output available on eBay for dirt cheap (or free if you have PC hobbyist friends or access to a typical corporate or edu recycle pile). Arcade cabinet games which output to CRT monitors stopped being made by around 2005 and game consoles which hooked to CRT TVs ended with the sixth generation (PS2, Gamecube, Dreamcast). This is good news because emulating the vast majority of arcade cabinet and console games up through the early 2000s doesn't require a fast GPU or CPU so using an older GPU with native analog output does everything you need (and saves a lot of money).
The last, best GPU made with native analog output was the Radeon R9 380x launched at the end of 2015. I have this card in my arcade cabinet emulation system (plugged into a 2014 HP ProDesk 600 G1 with i5-4590 Haswell CPU (~$70 used on eBay)). This PC is more than fast enough to perfectly emulate everything relevant to CRT gaming and the 380x GPU is substantial overkill. Being the last analog output card, the 380x is overpriced on eBay at >$50 but I only got it because I have a quite rare Wells Gardner D9200 quad-sync industrial CRT made specifically for arcade cabinets and that monitor is fairly unique because it can scan up to 38Khz (800x600 resolution). No games originally designed for CRTs use resolutions that high so it's only relevant for some PS2 games, and only then if I use non-authentic, 2x upscaling or HD texture packs in the emulator. So, I might theoretically, occasionally actually need the otherwise uselessly excess power of the 380x. If you're not me, just use almost any Radeon graphics card from 2012-2014 which can be had for ~$10-$15 to drive your CRT with GroovyMAME. Card compatibility list: https://emulation.gametechwiki.com/index.php/GroovyMAME). GroovyMAME forum: https://forum.arcadecontrols.com/index.php/board,52.0.html
> And are these tri-/quad-sync analog CRTs still manufactured?
All CRT manufacturing stopped around 2010. I was fortunate to buy my industrial-grade, quad-sync CRT new directly from the manufacturer in 2009. However, there are lot of used CRT TVs locally available from Craigslist and thrift stores, many of them for free or close to it. Higher quality CRTs like the Sony PVM and BVM series made for video production studios and broadcasters are now collectables selling for astronomical prices. However, high-quality consumer TVs from the late 90s and early 2000s, like Sony WEGA and any of dozens of models based on the well-regarded Sony BA-5 chassis, can be had in good condition for fairly reasonable prices. Many of these can also be modded to accept direct analog RGB input in addition to composite or S-Video, elevating their quality significantly higher (Modding Guide: https://sector.sunthar.com/guides/crt-rgb-mod/sony-ba-5.html). With the exploding interest in CRT retro gaming (for example: https://www.reddit.com/r/crtgaming), I'm surprised no one has yet restarted CRT manufacturing but CRTs are pretty complex beasts, essentially a kaiju-scale vacuum tube with arcane analog driver circuitry bolted on.
> I feel like modern television hardware is only just beginning to catch up
To be fair, with expanded color spaces, higher contrast, wide color gamuts (HDR10 etc), high-nits, faster gray-to-gray response times, black frame insertion and VRR, the latest, most expensive digital flat screen tech is getting closer in many ways. I can imagine it maybe getting there in the future but, unfortunately, the hardest part may be actually finding a modern television without ads, apps, online updates and DLC bloat.
Although I'm a retro purist and will never part with my beloved CRT-based emulation cabinet, I know not everyone is quite as obsessed or may not have space for such a system. So, it's important to also share that in recent years modern GPU-based pixel shader CRT emulation has gotten impressively closer to emulating analog CRTs, including shadow masks, analog glow, glass warping and even ray-traced bezel reflections. If you can't play on a real CRT, I encourage everyone to at least play games which were originally created for CRTs via CRT emulation. It's easy to do and retro pixel art looks so much better when presented as originally intended. See this image comparison: https://x.com/CRTpixels/status/1408451743214616587. Without CRT scanlines and phosphor glow, the art looks terrible and is just completely wrong. Check out Retroarch's shader community (https://forums.libretro.com/c/retroarch-additions/retroarch-...) and ReShade.
I only discovered that a lot of games output at weird refresh rates when I was putting together a mister. My vrr TV handles most of the weird refresh rates and resolutions but not all (in particular not bad dudes Vs the dragon ninja). I didn't know mk 1,2,3 run at 54 Hz! Mister doesn't have support for the mk boards so I've only played them via emulation on a pc, this means they have been running too fast! (I think)
One thing, my pc has a Nvidia 3070, if I tell retro arch to output at the original refresh rate (which my vrr TV should be able to handle) I'll get the correct refresh rate?
I think what you have been talking about is that post 2015, analogue output on graphics cards isn't natively generated so it's as bad as a hdmi to analogue adapter. Digital output to a vrr is completely separate.
Not necessarily. There are settings in MAME which provide some options on how to address frame rate mismatches. I think they all have various trade-offs like dropping, doubling or blending frames but I'm not current on what they are since all my serious retro gaming is on my CRT-based arcade cabinet :-). In theory at least, a modern GPU's ability to synthesize motion interpolated frames should allow fairly decent frame rate matching, even without VRR.
> if I tell retro arch to output at the original refresh rate (which my vrr TV should be able to handle) I'll get the correct refresh rate?
Yes. VRR is basically intended to do with a digital display what an analog CRT has always done, vary the display's refresh rate to match the source clock. However, I'll add a small caveat here. VRR is relatively new and advanced digital display features newly added to revisions of existing consumer video standards have a tendency to go through some teething pains as various device and display manufacturers figure out the nuances. I've only played around a little bit with VRR but haven't done any serious validation myself. Until it's more mature, I wouldn't assume correctness or compatibility of any recent addition to HDMI 2.1 (looking at you Source-based Tone Mapping!). So... trust but verify :-)
Also, since you mentioned Retroarch, here's a ProTip: Retroarch is admittedly convenient but for serious retro gaming I generally recommend using the original emulators directly, especially if you're striving for emulation accuracy and display correctness. MAME's interface is definitely more clunky and it's probably possible to achieve identical results with Retroarch but as a wrapper, it adds another layer of abstraction and potential for gremlins. There's also the potential for cores to not be up to date and the RA authors do change some things and make certain trade-offs to integrate disparate cores into their architecture. For CRT users I also don't know if there's even a GroovyMAME core for RetroArch.
This comes with the caveat that sometimes RetroArch's frontend is better than the standalone emulator's frontend -- RetroArch's graphics and input is quite mature and configurable on all platforms, and I've definitely had problems with bugs or latency in some less-maintained standalone emulators that aren't a problem when running through RetroArch. But yeah, agreed otherwise -- RetroArch is another layer between you and the emulator core that doesn't always do what you want or expose the options you need.
The layer of abstraction point you make is spot on, I've been using my steam deck a lot, I'm using emu deck which installs emulation station which installs retro arch. Configuration is scattered everywhere.
I haven't mucked about much with individual emulators in a while, so I'm not sure if they'll support run ahead latency reduction features, that's the one big thing I like in retro arch.
Edit: my main issue currently is figuring out what settings I should be using for particular cores/emulators. The steam deck screen isn't vrr, but it does allow refresh limiting. So that is its own set of problems. Similarly I think I'm using the right settings for my pc vrr set up, but never certain. Actually, I spend more time fiddling with setting Vs playing games!
No power grid I know of runs at 30Hz. North America (where NTSC was designed) and a few other places[0] run at 60Hz.
[0] https://en.wikipedia.org/wiki/Mains_electricity_by_country
A bit unrelated, but the links to your books at your website are no longer working. I tried to connect to you via email for this issue. Is this intentional or you will fix them?
Best regards, Ivan Bobev
This SNES video analysis one is incredible. I've always had all of this stuff running around in my head for how to explain how weirdly cool video generation for NTSC is, and you have done an incredible job finding a way to do so.
There is yet another reason for the weird frame and horizontal scan rate. When NTSC was originally introduced as a broadcast standard over a single RF modulated signal, the sound carrier and signals were also embedded in the signal as well. [1] Actually, I just found that Wikipedia does a good job of describing this on the NTSC page [2]:
When a transmitter broadcasts an NTSC signal, it amplitude-modulates a radio-frequency carrier with the NTSC signal just described, while it frequency-modulates a carrier 4.5 MHz higher with the audio signal. If non-linear distortion happens to the broadcast signal, the 3.579545 MHz color carrier may beat with the sound carrier to produce a dot pattern on the screen. To make the resulting pattern less noticeable, designers adjusted the original 15,750 Hz scanline rate down by a factor of 1.001 (0.1%) to match the audio carrier frequency divided by the factor 286, resulting in a field rate of approximately 59.94 Hz.
[1] https://upload.wikimedia.org/wikipedia/commons/f/fd/Ntsc_cha... The combined spectrum of video, sync, and audio all on a single RF broadcast signal.
[2] Search for 'sound carrier' in https://en.wikipedia.org/wiki/NTSC#Color_encoding
The highest frequency generated in a black and white TV was the horizontal scan rate, which was a multiple of the frame rate. With the addition of the NTSC color signal, which used a 3.579545 MHz carrier wave, the highest frequency generated in the TV became much higher. To keep the hardware simple, all lower frequencies were still divisors of the highest frequency, now color carrier wave. For the frame rate, it came out to 59.94 fields per second.
This one hits home. Although my examples are not specific to the Super Nintendo, it reminded me of the first time I played/watch Sonic the Hedgehog on the Mega Drive (Genesis)
I wasnt impressed with the game. It looked clunky and just felt slower compared to the Master System version. It wasn't until the rise of youtube I realised the difference in speed between the NTSC and PAL is huge. Its not just the speed of the game, but the Music. It sounds horrible on PAL!
Don't get me wrong - I knew about the PAL during the 16-bit, and the need for the "black box" but I didn't realise how much of a difference it was. I am sure the console magazines at the time would say the difference is minor in most games. One of the exception (honesty) was DooM on the SNES. The NTSC version had a bigger screen.
I remember being good at Punch-Out when I was a kid on the NES. I could beat Mr. Dream (or Mike Tyson) in the first round. Of course, I was playing the PAL version. If there was some kind of competition in the USA, I would have been destroyed in the first round! I would have been convinced I was framed!
Past times, right?
The NES/SNES minis always use the NTSC versions of the game, regardless of region.
Fixed that for you.
I get that the game speed depended on the framerate, but playing music at a frequency reduced by 17% would have sounded really horrible, I don't think they would have gotten away with it. But then again, what do I know... The only system I know a bit about is the Amiga, which had dedicated sound hardware, so I'm pretty sure it was not tied to the video frequency, no idea about other systems.
- The 3-button game controller is horrible, and the D-PAD is worse! - The main mascot game (Sonic the Hedgehog) was clunky with poor music
Of course, if I had experienced the Genesis on an NTSC then my initial view of the machine might have been totally different!
Overall many games I played in the UK - no matter the console... I was happy because I had nothing to compare it to. It's just Sonic the Hedgehog, from memory, was the main one that just felt off. I would not have thought it was a PAL vs NTSC thing.
Seems crazy games would be sold while so different, although it makes perfect sense why the choices were made.
As a kid I had just always assumed Mario was Mario and Sonic was Sonic everywhere. Why would they be different?
Was it the 3D consoles when this finally ended, since rendering and logic were no longer in lockstep most of the time?
Also, the developers properly adjusted Samus's physics constants and animation timings for the new framerate, but they didn't adjust enemies, cutscenes, or other aspects of the game environment. So Samus moves at the same speed as on NTSC, but the rest of the world moves slower. This means that on PAL you can grab Bombs and escape the room just in time before the door locks, skipping the miniboss fight: https://www.youtube.com/watch?v=R3t8TIIj7IM On the NTSC version, that same skip requires a complicated setup and several dozen frame perfect inputs in a row, and only one person has ever managed to pull it off: https://www.youtube.com/watch?v=jcKUMk5g8Wk
Here's a comparison of the fastest tool-assisted speedruns between NTSC (left) and PAL (right): https://www.youtube.com/watch?v=KD_-thqcB5s Both runs take the same route up until the very end; the NTSC version is faster in almost every single room, but PAL ends up finishing first because the arbitrary-code-execution setups are very different. The NTSC run has to do a very slow sequence of pausing and unpausing to move through a door without activating it, in order to get out of bounds and trigger memory corruption. Whereas on the PAL version, we're able to exploit a race condition in the game's animation system to achive ACE fully inbounds. The race is between a spike's knockback timer and Samus's landing animation; because Samus's timings were revised for PAL but the spike's were not, the timing works out a little differently and the race ends up being exploitable in this context on PAL but not on NTSC.
So when the Dreamcast came along, it was the first to offer games that you could switch between 50Hz and 60Hz but only if your TV could handle it. It also meant that with a lot of games that didn't account for this, you could make things easier by switching back to 50Hz. I recall Crazy taxi being much easier at 50Hz.
The SNES has a dot rate of ~5.37 MHz which is slower than the square pixel rate defined by the ATSC standards of ~6.13 MHz. It's exactly 8/7 slower, so pixels are stretched horizontally by 8/7, causing the 8:7 resolution to be stretched to (8/7)*(8/7)=64/49, which is close to 64:48 = 4:3.
> Result in an aspect ratio close to 4:3. This would mean 224*(4/3) = 298 visible dots.
If you consider what I mentioned, the factor would be (4/3)/(8/7) = 7/6, so they would have to choose something closer to 224*(7/6) = 261.33... visible dots. Which is much closer to what they chose with 256.
So with a coprocessor you can render your own frames and put them in memory where the next line’s tiles are going to be pulled from. That is what the SuperFX did, I think.
But in the end you’re still stuck with the limitations of the PPU actually drawing it in pixels and number of colors and such.
It was a painful experience! I don't recommend it.
Also this article was wonderful in the way that it didn’t waste a word. Very concise.
I LOVED SNES and was unfortunately never able to convince my immigrant parents to buy me one
Thank you for the writeup. Super interesting
The most reliable thing to do is probably to play through the entire game in an emulator (maybe from a TAS movie) and record whether it actually enables high-res mode or not.
Doesn't that block low frequency signals (e.g. an all-blue screen)?
Eh, jus try Super Mario World with an emulator on PAL settings with an NTSC ROM.
The counter and music will go much faster.
This is, as far as I can tell, an understatement - almost all TVs in europe offered SCART ports, the standard just originated from france.
I've read that it could even do HDTV in theory because it had YPbPr lines, but this was was never seriously attempted/rare in practice.
Other than the crazy size of the cable, seems like quite a big improvement over our random assortment of cables we went through over the years with composite -> s-video -> component.
I would first be shocked to see the smaller two-pronged electrical plugs in the flesh. Then I might be in trouble with the law if I walk across a road. And finally lose my mind over the fact that asking for 'tea' gives me something else entirely!
[0] found a photo of a period TV, not specifically ours http://www5.picturepush.com/photo/a/5316953/640/5316953.jpg
Carving - Suggests that material is only being removed, with excess being thrown away.
Tailoring - Suggests a mix of removal, addition, and general re-shaping, to fit a unique set of constraints for a customer.
I think jihadjihad might be on to something. Maybe this is a European English usage?
(I'm an American English speaker.)