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Some additional 680x0 FPU fixes allow us to load and view wireframes in Strata StudioPro, a popular early 3D modeling program for the Mac. (Strata was used to render the graphics in Myst).

[Linked Image from rbelmont.mameworld.info]

2 members like this: RowanD, Duke
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Here's a mildly amusing case of a NES bootleg. As you may recall the original Japanese Super Mario Bros 2 was only released in Japan on the Famicom Disk System. It was, however, heavily bootlegged on cartridge and on multicarts. One such bootleg can be seen running on hardware here: SMB2 (LE10). You'll observe something strange right away: the status bar at the top scrolls with the game! Additionally if you make it to the end of the video you'll see the game apparently freeze on a black screen.

Now, this title has run in various emulators for years (in MAME sadly it's always been just a grey screen) and none of them AFAIK exhibit the real hardware bugs; the status bar stays nicely fixed, and players talented enough to make it to World 4-4 are pleasantly greeted by World 5-1 after finding out their princess is in another castle. Why? Because, not knowing how the cart actually behaves, clever folks deduced that the number of CPU cycles between VBLANK and the end of the status bar was about 5750. At least that got the game running smoothly so all was good.

Your humble narrator comes into the story at this point. In an attempt to get this game running in MAME I *also* mucked around with values around 5750 and had it running smoothly. I almost submitted a patch with a nice formula: PPU cycles * (# of lines after VBLANK + status bar height) per 3 CPU cycles etc etc. It occurred to me though, all the other bootlegs of this game have 12-bit IRQ counters. It further occurred to me that bootleggers like to borrow the work of other bootleggers. It further further occurred to me that bootleggers don't typically take pride in polishing up their handiwork and may not even had somebody around who was good enough at this tough little game to play test to the end of 4-4, even with warps!

It may not be the final word on this bootleg, maybe krzysiobal over at NesDev will give us a nice schematic someday soon, but in the meantime—with any luck and the blessing of the MAME devs—enjoy a nice SMB2 bootleg, 12-bit IRQ counter, broken status bar, and crashing at the end of 4-4 like the bootleggers...intended?

Last edited by kmg; 07/26/21 06:26 AM.
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That's great, kmg. Running as badly as hardware seems counterintuitive but it's always the right way.

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Just submitted a couple of N64 fixes via pull request.

8bpp mode for framebuffers was completely nonexistent. After some back-and-forth with some N64 test programs courtesy of krom and my 64drive, it matches a real N64's output almost exactly:

[Linked Image from i.imgur.com]

There's some difference in gamma, but beyond that, it seems to work. Bit interesting in that the VI still scans the framebuffer out as 16bpp 5:5:5:1 pixels, but the neighboring 8-bit values that exist in the framebuffer effectively get paired together. I suspect if the test drew fill-rects with an odd number of pixels rather than even, we'd see a fringe of "wrong" colors on one or the other side of each column.

It also turns out that the "Magic Matrix" used for some dither operations was transposed along its axis. Fixing that fixes the dither patterns used in krom's AlphaCompare test:

[Linked Image from i.imgur.com]

2 members like this: kmg, R. Belmont
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Making progress on the only known Positron 9000 to exist https://binarydinosaurs.co.uk/Museum/Positron/index.php

It's the first time I've seen a SAA5050 being used to generate 80 columns.

[Linked Image from i.imgur.com]


BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, etc.
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Support for SPI SD cards was recently added by R. Belmont and used for an Apple II SD card device. The "BennVenn SD Loader" for the VZ-300/VZ-200 appreciates it:

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]

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