I've not used M1 recently so I might be wrong, but IIRC it has an ini file and a 'rompath' option in it... EDIT: see start of this topic! It's a [ROMPATH] section actually.

This is the critical point.

On my Rooted Galaxy S2, i don't see any .ini file to edit :\

I also tried to create manually the m1.ini file, but m1 android doesn't see any roms in the path specified in the .ini file

It assumes an SD card; I'm not sure if it works on devices without one.

It worked fine for me when I just followed the instructions. Due to quirks of Android, even devices with no SD card will still have a virtual SD card.

I have the sd card, and i installed on it, but no ini file appears and if i create it, it doesn't work.

Any ideas?

There is no .ini file to deal with. In the M1 interface, you press your Menu button on the phone/tablet and selec the Open option. You will be presented with a list of ROMs you have in the "roms" folder I mentioned above. You can press on any one of them to start playing it.

Note: As of Android 4.0 and later, some songs do not play properly even if you specifically uncheck "Use List Song Length". This is a known issue.

Also, do not ever press the Stop button. It will cause M1 to hang on all versions of Android. It will be removed and replaced with a "restart song" button in the future according to neko68k.

So, if i already have a mame romset on my device to play, i have to put another romset tu have all songs with m1, right?

No, with an up to date m1.xml file you can use up to date MAME ROMs.

skipping roms version issue (by the way, what romset version i have to uae?), i was talking about have just ONE romset in ONE directory, mame4all and m1.

Is it possible?

It should be; it sounds like maybe Android M1 can't have a configurable rom path (the original PC versions can) but mame4all certainly should have that option so you can point it to M1's directory.