Diff MAME version of Musashi with current

[emoon]

There seems to have been a fair amount of changes over here at the MAME repro

https://github.com/mamedev/mame/commits/115ffcb10a45bca233fa6e22f674d8db8982b7df/src/emu/cpu/m68000

It might be worth taking a look and diff against the current one (here https://github.com/kstenerud/Musashi ) to make sure we don't implement something in bad way.

I don't think many of the MAME changes has made it back to the original repro.

[marhel]

Very interesting! I completely agree it's worth checking out!

[emoon]

👍

[marhel]

And the other way around, MAME still have the ADDA bug, it seems. https://github.com/mamedev/mame/blob/master/src/devices/cpu/m68000/m68k_in.cpp#L1248-L1254 and https://github.com/mamedev/mame/blob/master/src/devices/cpu/m68000/m68k_in.cpp#L1273-L1279 should evaluate OPER_AY before AX...

[emoon]

Ah.. Interesting :)

This is something that one needs to make sure of to handle also:

mamedev/mame@b025f69

[emoon]

For the disassembler I found quite a bit of issues as well when I worked on this

https://github.com/aquynh/capstone/blob/next/arch/M68K/M68KDisassembler.c

I know I submitted a few changes back but I missed quite a few I'm pretty sure of

[emoon]

Oh btw. Notice this clr on 000 mamedev/mame@844e696

[marhel]

I've noticed that as well, but didn't care for now, as I feel it would only affect "real-world" devices.

[emoon]

Yeah I guess that is true.

[emoon]

And I guess this is taken into account with the cycle count? As I would assume this would make clr slower but I may be wrong.

[marhel]

If we where to add more accurate cycle counting based on actual RAM-accesses etc, then yes we would need to account for one less read-cycle. Today if the opcodehandler first access RAM (which should costs 4 cycles I think) and then cause an exception, we act as if the instruction was in fact "for free" and only count exception cycles. In real life, the actual cycles taken would depend on how much work the instruction had done before the exception happened, but cycles are not accounted for on that level.

[marhel]

Obviously a "fixed" implementation of CLR would do one more memory read, which would take non-zero time in the real world.

[emoon]

Yeah I wonder if a move (with a dn register set to zero) would be faster in the real-world then compared to a clr

[emoon]

I might actually test it at some point and see :)

[marhel]

Ah, you meant real-world CLR, yes this "feature" makes the instruction 4 clocks slower than absolutely necessary, which you should be able to see if comparing the cycle counts for CLR in the 010, which doesn't do a useless read first.

[emoon]

Yeah I just wonder if a move d0,(a0)+ would be faster than clr.w (a0)+ in the real-world.

[marhel]

Well, either way that should be evident if you compare cycle counts for the two, see the M68000UM section 8, which I don't have time to do now ;)

[emoon]

Yeah, will do :)

[emoon]

Looks like its taking the same amount of cycles (12)

[marhel]

Oops, they have fixed the adda-bug, I now notice!

[emoon]

Ah :) Yeah it would be interesting to just diff the code but it seems they have C++:ified the code so that might prove a bit hard :/

[marhel]

I took a look yesterday, and there seems to be history back to dec 2007, using Musashi 3.31 according to the source code. In particular, one interesting change, is fixing the dependencies on global functions preventing the use of several different Musashi-cores at the same time. Remaining global functions takes a CPU-core as an argument, I think.

Maybe, with some work, it would be possible to both use latest MAME-Musashi (4.90 i think), which I guess would include a few fixes not in https://github.com/kstenerud/Musashi, as well as remove the globals-depencencies that force us to serialize Musashi access with a MUTEX. This would improve test performance greatly, allowing multithreaded tests.

Don't know how much dependencies to the rest of MAME that has crept into the codebase, though.

[emoon]

Yeah that would be nice. I really never liked that Musashi has global functions with no context so yes that would be nice to get it.

As MAME is multi cpu I would imagine they keep the code fairly separate and just don't throw lots of specific stuff in there but you never know.

[emoon]

You didn't find any other opcode specific fixes? (I haven't looked myself)

[marhel]

No,, but I didn't spend too much time looking either. It seemed that the adda fix was just a side effect of removing a lot of macros. Several fixes to 020+ though, including actually emulating 020+ and ColdFire

[emoon]

Alright. Good to know.

[marhel]

And I think they added some more event callbacks (one for TAS in particular, which apparently uses a different bus-cycle in real-world, which can have HW-side-effects which might need to be emulated), as well as allowing bus errors to be triggered externally, and some fixes to exception stack formats IIRC.

[emoon]

I see. I guess some Arcades/games may have relied on it (both by intention and non-intention)

[marhel]

Good guess. They specifically mentioned two games that actually depended on the TAS write not to succeed (apparantly, the callback allows the host to specify if the write should be allowed or not).

[emoon]

Ah I see... Must have been "fun" to track down :)