-- I try to keep up with the MAME and MESS devs, but it's not always a simple task. Anyway, QMC2 is around for a long time already, and I plan to keep it that way...
@Anna: thanks for the report and screen shot! It's likely a bug... I have to check. And yes, the "Devices" tab is supposed to do the job you want to achieve. There was a bug prior to SVN r2670 (see http://sourceforge.net/apps/mantisbt/qmc2/view.php?id=17
), but it should work again now (with the build you're using).
What you have to do:
0) optional/recommended: click the "Configuration" button and select "Default device directory for '<machine-name>'..." so you can point QMC2 to a "primary" directory where you have your cart/rom/bin/whatever files for the current system (machine in "QMC2 jargon"). This directory will later be presented to you when you "browse" those files...
EDIT: note that the second item - "Generate configurations for '<machine-name>'..." - is a not yet implemented WIP feature.
1) click the only "enabled" button right to the device name ("No devices") to create a new empty device setup
1a) if you're going to use device files with speaking names, don't bother with setting up a name for the configuration... QMC2 will automatically do it for you -- see 2)!
2) from the (then enabled) list of available "Device instances" select the one (or more) you want to map a file to; when you click the browse button, the default directory from 0) will be used, filtered by the names that fit the "Extensions" column.
3) When you've selected a file this way, QMC2 will suggest a configuration name (when the name is still not set, that is).
4) When you're done with the setup, click the "save" button (right-most tool button, now enabled as well!)
5) The configuration will be added to the list of "Available device configurations" and can then be selected and "played"