Undefined behavior for ABCD and SBCD

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r57shell
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Re: Undefined behavior for ABCD and SBCD

Post by r57shell » Thu Apr 27, 2017 2:32 pm

HardWareMan wrote:I do not understand, hasn't anyone looked at the CPU die shots yet?
Basic die shots. Then, Quietust has made a great contribution by isolating the metal traces. Olivier Galibert was able to make use of this layer image, with a few corrections, to produce a full transistor-level schematic of the 68000. In result, here the interactive map. You can look at ALU under the magnifying glass. I don't see any problem in getting true behavior without guessing.
After hours of pain, was able to compile https://github.com/galibert/dietools.git using Visual Studio 2010
Not all...
logx was failed to compile because of C++11 syntax.
mscheme probably bugged compilation because I had to implement what is not defined in LuaJIT.
sview a bit modified to make pins text work + vcc/gnd voltage change. In repo vcc & gnd voltage forced to 0, otherwise you'll get tons of errors "Unhandled equation system." :lol:

So. For anyone who wanna play with it:
1) Download scheme: https://og.kervella.org/m68k/schem.txt
2) Download deietools (my build): http://www.mediafire.com/file/2p5giq3fs ... ietools.7z
3) Unpack in some dir
4) Open cmd.exe there, run: sview "path_to_schem.txt". Or simply drag schem.txt and drop over sview.exe
5) ?!?!?
6) Have Fun!
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notaz
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Re: Undefined behavior for ABCD and SBCD

Post by notaz » Wed Sep 20, 2017 7:48 pm

Small update to flamewing's test to trigger a bug in Genesis-Plus-GX at least:
https://github.com/flamewing/68k-bcd-ve ... e3afd720bf
http://notaz.gp2x.de/md/rel/bcd-verifier-u1.zip

Eke
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Re: Undefined behavior for ABCD and SBCD

Post by Eke » Sun Sep 24, 2017 10:41 pm

notaz wrote:
Wed Sep 20, 2017 7:48 pm
Small update to flamewing's test to trigger a bug in Genesis-Plus-GX at least:
https://github.com/flamewing/68k-bcd-ve ... e3afd720bf
http://notaz.gp2x.de/md/rel/bcd-verifier-u1.zip
Well, this was indeed a very stupid bug in Musashi: upper bits of NBCD source operand were not masked when it comes from a 68k register, which would lead to incorrect calculation when those bits are not cleared before calling the instruction. Thanks for the notice.

mikro
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Re: Undefined behavior for ABCD and SBCD

Post by mikro » Tue Jan 09, 2018 12:52 am

Hi there,

a newcomer and non-Sega guy here. :) I found this super interesting thread, thanks for all the published code. It will help me a lot. However:
flamewing wrote:
Sun Mar 19, 2017 4:02 pm
So, I decided to conduct my own investigation into this issue, and did some HW tests, patent investigation, and number crunching; and after doing all that, I discover this thread, in which I confirm my findings that every single emulator does it wrong.
this is true only for Sega emulators I guess. UAE-based emulators (incl. Atari ones like Hatari or Aranym) do that nearly 100% correct -- only a few cases of NBCD's V flag are wrong.

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flamewing
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Re: Undefined behavior for ABCD and SBCD

Post by flamewing » Thu Jan 11, 2018 8:27 am

mikro wrote:
Tue Jan 09, 2018 12:52 am
this is true only for Sega emulators I guess. UAE-based emulators (incl. Atari ones like Hatari or Aranym) do that nearly 100% correct -- only a few cases of NBCD's V flag are wrong.
Thanks for confirming that even the non-Sega emulators also got the BCD instructions wrong :-)

(even if only slightly)

By the way, BlastEm (and I think GPGX) now emulate these instructions correctly.

And welcome to the forums!

mikro
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Re: Undefined behavior for ABCD and SBCD

Post by mikro » Thu Jan 11, 2018 9:12 am

flamewing wrote:
Thu Jan 11, 2018 8:27 am
Thanks for confirming that even the non-Sega emulators also got the BCD instructions wrong :-)

(even if only slightly)

By the way, BlastEm (and I think GPGX) now emulate these instructions correctly.
Not anymore. :) Thanks to your code I was able to spot the slight error in WinUAE, then the change got merged into Hatari virtually straight away.

By the way, the reason why I started with those experiments is that I'm trying to find out how much feasible is to use ABCD/SBCD to 6502's ADC/SBC instructions emulation in the decimal mode (I mean mainly the carry flag and result as the other flags are handled differently).

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