21 March 2020, 07:50 | #21 |
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@eastrayk that’s a super impressive video the speed is remarkable
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21 March 2020, 08:46 | #22 | |
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NO WAY!!! BTW, really impressive emulator! OK, 16MHz is more than twice as fast as a 7-ish MHz 500 but still I reckon that THIS is how a speccy emulator should look on such machines! Thanks to our friend from Spain for the nice video!! |
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21 March 2020, 08:54 | #23 |
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...and, hey, does this run on a stock 520ST?
We could try it then through Amtari/Medusa/Chamaeleon on our 500s, hahaha!! |
21 March 2020, 08:57 | #24 | |
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but the video update will be an issue for sure. Getting the source code and porting it would be the best way. |
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21 March 2020, 10:52 | #25 |
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You could probably get a pretty good emulation going if you had the emulated CPU just write to a monochrome bitmap and completely ignored the Speccy's color map. I don't know what happens if you tell OCS that your horizontal width is smaller than 320 though. If you can't have a 256-pixel wide bitmap in OCS, you could feed it the 256-wide bitmap to a 320-pixel wide display and get around this by having the copper reset the display to the correct position every scanline and use sprites to cover the garbage on the side of the screen.
EDIT: Obviously either way the pixel clock/aspect will be wrong, but you can just fix that with the dials on your monitor. Last edited by AmigaHope; 21 March 2020 at 10:59. |
21 March 2020, 12:14 | #26 |
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amigahope that could be perfect for those isometric games that can't change colors except in status bar, so playfield is monochrome anyway.
maybe copper could be used to emulate colors. I don't know the speccy, I had this idea for the Oric but wasn't doable in all cases because copper cannot switch colors fast enough Last edited by jotd; 21 March 2020 at 13:16. |
21 March 2020, 13:46 | #27 |
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Actually, on further thought, you would have to do copper tricks anyway because the Speccy's bitmap layout is weird (scanlines are staggered in memory).
...but thinking even further, there could be bit-endianness problems. It *shouldn't* be a problem because emulation code usually converts endianness in bitwise operations so that bytewise operations can be emulated faster (same with word-endianness) Copper color-change idea wouldn't work because you can change one color register every 8 pixels, but emulating speccy colormap would require two register changes every 8 pixels. Plus the overhead of modifying the copperlist in horizontal blank. I guess it would work for games where the background color stays the same and only the foreground color changes. Last edited by AmigaHope; 21 March 2020 at 14:06. |
21 March 2020, 14:50 | #28 |
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ironic that those 8 bits machines could switch colors faster than the copper can, with 1 bitplane.
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21 March 2020, 17:28 | #29 | |
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If we really think about it, it is curious that this ST emulator from 1990 works perfectly with 16Mhz and nowaways we need a minimum of 1000Mhz to be able to emulate any machine. Either things were very well optimized before or now we do them very badly? This is a hidden video, in response to a user of a Spanish forum where he was laughing at the alleged multitasking that did not exist in the Atari ST operating system. To show him that there were other alternative operating systems on ST, I made a video where I run a fully assembly operating system called MagiC for ST. Multitask and displaying some applications running at the same time, like the spectrum emulator. The video is in Spanish but what matters is that you see that it also works at the same speed in monochrome. 640x400. Atari MegaSTE 16Mhz. [ Show youtube player ] |
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21 March 2020, 17:57 | #30 |
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nowadays 8-bit emulators are often written in C for portability. They also perform full screen refresh, with pixel by pixel computation, double buffering, also in C.
With asm you can directly convert N,Z,V,C flags between processors. In C you have to re-do the computation. That's one of the advantages, but not the only one, of writing an emulator in asm, with tricks for partial refresh and all. note that Mame4ALL uses some asm cpu cores (arm) for z80 and others. Mame4all works well at 60 fps on very old android/iOS devices. even in assembly, emulating a speccy with proper speed on a 68000 is a miracle. |
21 March 2020, 18:23 | #31 | |
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Also on the Amiga there is no "slowdown" if you don't use the Blitter. The speed of memory operations is the same for the ST and the A500 and is limited by the 68k ... the only difference is the clock 8 vs 7 MHz. With a 16MH/14MHz 68K you would need real fastRAM on the Amiga or some cache (16KB) like the MegaSTE |
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21 March 2020, 18:40 | #32 |
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well, code running from chipmem is super slow regardless if you're using the blitter or not. Data read/writes are following the same rules.
I'd be glad to be wrong |
21 March 2020, 18:42 | #33 |
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Remember that horizontal resolution of a speccy is 256 pixels, that should help to recover a bit of bandwidth (maybe)
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21 March 2020, 19:05 | #34 | |
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There is no slowdown for 4-bitplanes (or 2 high res) , speaking 16 colors, since the 68000 needs four clock ticks per memory access anyways. That allows for the interleaved RAM access on BOTH computers. only with more colours or Blitter-operations the chipset will block the cpu. |
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21 March 2020, 19:44 | #35 |
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21 March 2020, 20:50 | #36 |
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21 March 2020, 21:03 | #37 | |
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22 March 2020, 09:01 | #38 | |
Amiga? What's that?!?
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I just wonder, no equipment to test t here... |
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22 March 2020, 09:55 | #39 | |
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Current emulators aim to be 100% accurate, and that requires a lot more CPU power. |
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22 March 2020, 16:21 | #40 |
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You're right. I mean it works perfectly for 95% 80's Spectrum games.
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