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Thread: Genesis 3 with TAS bug?

  1. #1
    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    Default Genesis 3 with TAS bug?

    I recently got an everdrive, and run a test program on my model 3 Genesis. One of the program's functions is to check whether or not the Genesis it is running on has the "TAS" bug or not. If you don't already know, the "test and set" instruction supposedly doesn't work on any Genesis except the model 3.

    Strangely, I loaded the program up, and it told me that my model 3 did in fact have the TAS bug, which is strange because I though they fixed this error in the model 3 revision. I thought maybe I just didn't program it correctly, so I loaded up the gargoyles game, which supposedly doesn't work on the model 3.

    Here is what segaretro.org says on the gargoyles page:
    The game uses the MC68000's tas (test and set) opcode to do condition-related things. tas runs in a different way from other CPUs, and for some unknown reason the Genesis is wired differently. The designers of the Genesis 3 overlooked this, and for some unknown reason, the game will not run on this model, making it the only game not to run on the Genesis 3 due to something other than additional hardware not being supported.
    And on the Model 3 page:
    A bug in the console's I/O controller that prevented the "TAS" instruction from working correctly was fixed in the Genesis 3. However, some games that incorrectly used this instruction, such as Gargoyles, will no longer run correctly, since they expected the instruction to do nothing.
    I was surprised to see the Gargoyles game load up and run just fine. I played for about 5 minutes before I shut it off.

    My model 3 is a VA1 revision. Is it possible that TAS was only fixed in the VA2 revision? I also applied the Game Genie and Virtua Racing compatibility fixes, but I don't think that would also re-break the TAS instruction, would it?
    Modded consoles:
    Master System (v7040) with s-video & direct AV out
    Model 1 with 10mhz overclock & halt switches
    Model 1 with 10mhz 68010
    Model 2 VA2.3 with unfiltered Mega Amp, & s-video
    Model 3 VA1 with compatibility fixes & s-video
    32X with s-video
    Visit my web site at www.mode5.net
    Or my collection of homebrew Genesis games, programs, and music on SEGA-16!

  2. #2
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    I have a what I'm guessing it's a VA2 coming next week, I'll check Gargoyles on my ED too. What's the name of the test rom you are talking about? Is it available?

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    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    Quote Originally Posted by chilled View Post
    I have a what I'm guessing it's a VA2 coming next week, I'll check Gargoyles on my ED too. What's the name of the test rom you are talking about? Is it available?
    It's something I made, and really need to release already.
    Oh well, I guess I'll just post it here! It's a whole bunch of tools in one, and the 'TAS test' is just one of them. You'll see the TAS info on the screen when it first boots up.

    Download link:
    https://drive.google.com/file/d/0B-u...ew?usp=sharing

    Interestingly, I tried a really old Genesis emulator, and it reported TAS as working.
    Modded consoles:
    Master System (v7040) with s-video & direct AV out
    Model 1 with 10mhz overclock & halt switches
    Model 1 with 10mhz 68010
    Model 2 VA2.3 with unfiltered Mega Amp, & s-video
    Model 3 VA1 with compatibility fixes & s-video
    32X with s-video
    Visit my web site at www.mode5.net
    Or my collection of homebrew Genesis games, programs, and music on SEGA-16!

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    Quote Originally Posted by ComradeOj View Post
    My model 3 is a VA1 revision. Is it possible that TAS was only fixed in the VA2 revision?
    Yes, Tiido confirmed this back in 2010. (model 2 VA4s & Genesis 3 VA1s both use the Yamaha FJ3002 ASIC)

    Quote Originally Posted by ComradeOj View Post
    I also applied the Game Genie and Virtua Racing compatibility fixes, but I don't think that would also re-break the TAS instruction, would it?
    No, you'd need to alter the 'DTACK' & 'AS' lines.

  5. #5
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    I just recieved a stock Genesis 3 VA2 (I opened to check) and Gargoyles doesn't work (neither does Cliffhanger btw: they run but they glitch pretty soon) so the TAS bug is corrected at least in this model.

    A bit offtopic but:
    Also the RGB video ouput is saturated just as my two model 2 consoles (PAL v1.8 and Genesis VA4). This doesn't seem to be reported anywhere. I mean saturated both in traditional CRT and video projector outputs (the first without any upscaling and the second via SCART to hdmi generic converter) in comparion from the RGB output I get from my model 1s (Genesis and PAL VA6s) which is not saturated.
    It bothers me a lot because there are not enough settings on my systems to adjust that (contrast & brightness do not solve the problem at all) and I read everywhere that model 2 VA4 and Genesis 3 are supposed to have good video output (that is true for the composite btw, I checked) and that RGB is supposed to be the same for all models (because there's no encoding) but THIS IS NOT TRUE : all my model 2 & 3 RGBs are saturated whereas model 1s are not.
    Last edited by chilled; 06-14-2015 at 09:12 PM.

  6. #6
    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    Quote Originally Posted by chilled View Post
    I just recieved a stock Genesis 3 VA2 (I opened to check) and Gargoyles doesn't work (neither does Cliffhanger btw: they run but they glitch pretty soon) so the TAS bug is corrected at least in this model.

    A bit offtopic but:
    Also the RGB video ouput is saturated just as my two model 2 consoles (PAL v1.8 and Genesis VA4). This doesn't seem to be reported anywhere. I mean saturated both in traditional CRT and video projector outputs (the first without any upscaling and the second via SCART to hdmi generic converter) in comparion from the RGB output I get from my model 1s (Genesis and PAL VA6s) which is not saturated.
    It bothers me a lot because there are not enough settings on my systems to adjust that (contrast & brightness do not solve the problem at all) and I read everywhere that model 2 VA4 and Genesis 3 are supposed to have good video output (that is true for the composite btw, I checked) and that RGB is supposed to be the same for all models (because there's no encoding) but THIS IS NOT TRUE : all my model 2 & 3 RGBs are saturated whereas model 1s are not.
    Hmm, so it seems that only the VA2 had the TAS bug fixed? That makes sense. After all, the model 3 VA1 is basically a smaller model 2 VA4. I don't know about the RGB issue, sorry. I also thought RGB was the same across all systems.

    Were you able to test my homebrew program on your model 3 VA2? The download link is in this thread a few posts up from this one. The first screen will tell you if TAS is working or not.
    Modded consoles:
    Master System (v7040) with s-video & direct AV out
    Model 1 with 10mhz overclock & halt switches
    Model 1 with 10mhz 68010
    Model 2 VA2.3 with unfiltered Mega Amp, & s-video
    Model 3 VA1 with compatibility fixes & s-video
    32X with s-video
    Visit my web site at www.mode5.net
    Or my collection of homebrew Genesis games, programs, and music on SEGA-16!

  7. #7
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    Yes I did! TAS: working (model 3) Benchmark 3298 etc
    but it says page 1/9 but I can't scroll to other pages. Is it because it is WIP ?

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    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    Quote Originally Posted by chilled View Post
    Yes I did! TAS: working (model 3) Benchmark 3298 etc
    but it says page 1/9 but I can't scroll to other pages. Is it because it is WIP ?
    Thanks for testing it for me!
    No, it's totally finished. You have to hold A+the dpad to flip pages. You also can't use a 6 button controller unless you keep MODE held down.

    I really need to make a video and "release" the program already. It has a bunch of tools that people might find helpful, including:

    A tool to read any memory as display the data on the screen.
    A tool to write any data to any location in memory
    A simple sound test
    A controller test
    An exception test
    A benchmark
    A simple VDP test

    There is also a SEGA CD port, but it's lacking the benchmark and sound test. Otherwise it's all there.
    Modded consoles:
    Master System (v7040) with s-video & direct AV out
    Model 1 with 10mhz overclock & halt switches
    Model 1 with 10mhz 68010
    Model 2 VA2.3 with unfiltered Mega Amp, & s-video
    Model 3 VA1 with compatibility fixes & s-video
    32X with s-video
    Visit my web site at www.mode5.net
    Or my collection of homebrew Genesis games, programs, and music on SEGA-16!

  9. #9
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    it's a very promising software that's for sure.

    Could you replace the A+down control with a simple down (or left, or A button, but not combined) ? I thought it wasn't finished because I couldn't figure how to scroll... also I was using a 6 button japanese sega arcade stick so my chances were slim

    You also did a simple CPU benchmark only rom but I guess the one included here does the same job, isn't it?

  10. #10
    Comrade as in friend. Master of Shinobi ComradeOj's Avatar
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    Quote Originally Posted by chilled View Post
    it's a very promising software that's for sure.

    Could you replace the A+down control with a simple down (or left, or A button, but not combined) ? I thought it wasn't finished because I couldn't figure how to scroll... also I was using a 6 button japanese sega arcade stick so my chances were slim

    You also did a simple CPU benchmark only rom but I guess the one included here does the same job, isn't it?
    You only need to hold A when switching pages. When using the different sub programs, you don't have to hold anything. The reason for the odd control scheme is because of control conflicts. If you pressed left, the program wouldn't really know if you wanted to flip the page left, or move left in the sub program. The easiest fix was to make you have to hold A to flip pages and have everything else normal.

    The benchmark ROM I made is basically the same as the benchmark in my multi tool program. They both work by measuring how many times the CPU can run a loop containing various instructions in a given time. The only difference is, the multi tool program's benchmark has more instructions in the loop so it gives lower scores than my older benchmark program. Basically, a score of 3298 means that the CPU was able to run that loop 3298 times before the time ran out.


    Also, my Genesis modded with a 10mhz 68010 scored 4397. Beat that! My 10mhz 68000 Genesis got 4159
    Modded consoles:
    Master System (v7040) with s-video & direct AV out
    Model 1 with 10mhz overclock & halt switches
    Model 1 with 10mhz 68010
    Model 2 VA2.3 with unfiltered Mega Amp, & s-video
    Model 3 VA1 with compatibility fixes & s-video
    32X with s-video
    Visit my web site at www.mode5.net
    Or my collection of homebrew Genesis games, programs, and music on SEGA-16!

  11. #11
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    just ran the test on the Gens 15mhz version and I got 6177, hehe

    Road Rash and many racing games are greatly improved on this, far beyond any modded real hardware AFAIK

    Also regular Kega Fusion delivers "very" different results at each boot (between 3550 and 3660 or so), why is that?

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