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View topic - ROM -> VRAM bandwidth: 170KB/sec ANSWERED

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ROM -> VRAM bandwidth: 170KB/sec ANSWERED
Post Posted: Tue Mar 15, 2022 6:48 am
Last edited by maxxoccupancy on Wed Mar 16, 2022 2:11 am; edited 2 times in total
Does anyone happen to know how many kilobytes per second can be moved from the game ROM to VRAM per second? I've been reading every bit of documentation I can find and searching the fora, but I haven't found even a guess.

Answered, thanks. That's 91 tiles/frame in NTSC and 113 tiles/frame in PAL mode. For NTSC, that means that FMV could theoretically be played uncompressed at 30fps 18x10 tiles, or 144x80.

That does explain why games like Aladdin were able to play very large, well animated characters and even some 3D trickery like the sides of the building and background. It's strange that more games didn't take advantage of the powerful hardware on the SMS.


Number of bytes that can be transferred using Z80 (OUTI):
+------+--------+---------+-------+
| Mode | Active | Passive | Total |
+------+--------+---------+-------+
| PAL  |  1920  |   1724  |  3644 |
| NTSC |  1920  |    997  |  2917 |
+------+--------+---------+-------+
Number of tiles that can be transferred using Z80 (OUTI):
+------+--------+---------+-------+
| Mode | Active | Passive | Total |
+------+--------+---------+-------+
| PAL  |   60   |    53   |  113  |
| NTSC |   60   |    31   |   91  |
+------+--------+---------+-------+
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Post Posted: Tue Mar 15, 2022 7:28 am
https://www.smspower.org/forums/14599-HowManyBytesCanIWriteToVRAMPerFrame
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Post Posted: Wed Mar 16, 2022 8:55 am
note that to achieve those figures you would need to use 100% of the frame time to load tiles to VRAM, you probably don't want that.
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Post Posted: Wed Mar 16, 2022 11:49 am
maxxoccupancy wrote
Answered, thanks. That's 91 tiles/frame in NTSC and 113 tiles/frame in PAL mode. For NTSC, that means that FMV could theoretically be played uncompressed at 30fps 18x10 tiles, or 144x80.

That does explain why games like Aladdin were able to play very large, well animated characters and even some 3D trickery like the sides of the building and background. It's strange that more games didn't take advantage of the powerful hardware on the SMS.

Because ROM size was limited to 1MB by the existing mappers, and memory was expensive too.
Also it's very easy for us to manipulate data (e.g. convert a video to a bunch of tiles) with the processing power we have today.
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Post Posted: Mon Mar 21, 2022 4:07 pm
Apocalypse wrote
maxxoccupancy wrote
Answered, thanks. That's 91 tiles/frame in NTSC and 113 tiles/frame in PAL mode. For NTSC, that means that FMV could theoretically be played uncompressed at 30fps 18x10 tiles, or 144x80.

That does explain why games like Aladdin were able to play very large, well animated characters and even some 3D trickery like the sides of the building and background. It's strange that more games didn't take advantage of the powerful hardware on the SMS.

Because ROM size was limited to 1MB by the existing mappers, and memory was expensive too.
Also it's very easy for us to manipulate data (e.g. convert a video to a bunch of tiles) with the processing power we have today.


There are only a couple of 8 megabit games (Street Fighter II and Sonic Blast are the only ones I know of). However, game developers sometimes did have a $200,000 SGI workstation and some very impressive software, especially by the early 90s. An SGI GPro V12 was capable of about 500 MFlops and 2GB/sec of bandwidth. That's nothing compared to today's graphics cards, but more than enough to render the frames for Mickey Mania's rotating brick tower.

The impressive pre-rendered graphics on Vectorman and Adventures of Batman & Robbin tell me that much better could've been done for the SMS in 1992 when SEGA of Japan killed the system off. Subsequent games like Aladdin and Land of Illusion showed off what the SMS had been capable of all along.

I feel like the limit pushers could've gotten another order of magnitude performance out of the system, even using the workstations, dithering, and compression techniques available back in the day.

With a 32 megabit cart and the hardware and software available now, I believe we could produce games that are 10x better looking. Studying how Randy Linden got Doom onto the SNES using a CPU not much more powerful that then Z80A and a VDP that runs at the the same speed (using the same techniques that I suggested for 3D graphics), I feel like it must be possible to get some textured 3D on the SMS, albeit not as impressive as the SVP chip and Virtua games.

I always felt as though the SMS was capabale of much more than we ever saw.
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Post Posted: Mon Mar 21, 2022 4:49 pm
maxxoccupancy wrote
Apocalypse wrote
maxxoccupancy wrote
Answered, thanks. That's 91 tiles/frame in NTSC and 113 tiles/frame in PAL mode. For NTSC, that means that FMV could theoretically be played uncompressed at 30fps 18x10 tiles, or 144x80.

That does explain why games like Aladdin were able to play very large, well animated characters and even some 3D trickery like the sides of the building and background. It's strange that more games didn't take advantage of the powerful hardware on the SMS.

Because ROM size was limited to 1MB by the existing mappers, and memory was expensive too.
Also it's very easy for us to manipulate data (e.g. convert a video to a bunch of tiles) with the processing power we have today.


There are only a couple of 8 megabit games (Street Fighter II and Sonic Blast are the only ones I know of). However, game developers sometimes did have a $200,000 SGI workstation and some very impressive software, especially by the early 90s. An SGI GPro V12 was capable of about 500 MFlops and 2GB/sec of bandwidth. That's nothing compared to today's graphics cards, but more than enough to render the frames for Mickey Mania's rotating brick tower.

The impressive pre-rendered graphics on Vectorman and Adventures of Batman & Robbin tell me that much better could've been done for the SMS in 1992 when SEGA of Japan killed the system off. Subsequent games like Aladdin and Land of Illusion showed off what the SMS had been capable of all along.

I feel like the limit pushers could've gotten another order of magnitude performance out of the system, even using the workstations, dithering, and compression techniques available back in the day.

With a 32 megabit cart and the hardware and software available now, I believe we could produce games that are 10x better looking. Studying how Randy Linden got Doom onto the SNES using a CPU not much more powerful that then Z80A and a VDP that runs at the the same speed (using the same techniques that I suggested for 3D graphics), I feel like it must be possible to get some textured 3D on the SMS, albeit not as impressive as the SVP chip and Virtua games.

I always felt as though the SMS was capabale of much more than we ever saw.


Doom on SNES has the SuperFX chip on the cartridge, which has 6 times the clock rate of the SNES main CPU, plus hardware designed specifically for 3D; if you want to make something similar, you would need to add a CPU to the cartridge.
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Post Posted: Wed Mar 23, 2022 12:57 pm
haroldoop wrote
Doom on SNES has the SuperFX chip on the cartridge, which has 6 times the clock rate of the SNES main CPU, plus hardware designed specifically for 3D; if you want to make something similar, you would need to add a CPU to the cartridge.


There's a rather impressive attempt at converting Starfox to the Megadrive without any special chip:
https://twitter.com/gasega68k/status/1439076050068193286
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Post Posted: Thu Mar 24, 2022 4:26 am
Bock wrote
haroldoop wrote
Doom on SNES has the SuperFX chip on the cartridge, which has 6 times the clock rate of the SNES main CPU, plus hardware designed specifically for 3D; if you want to make something similar, you would need to add a CPU to the cartridge.


There's a rather impressive attempt at converting Starfox to the Megadrive without any special chip:
https://twitter.com/gasega68k/status/1439076050068193286


That is impressive. I knew that the 68000 was capable of hundreds of polygons/sec, but didn't realize that it could do thousands. I wonder if he used LookUp Tables and more economical floating point or fixed point values.
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