MESS and TI cartridges
In MESS there are two ways to emulate cartridges; the MESS emulation of the TI-99 system has a special one that may be used beside the general MAME/MESS-like concept.
TI Solid State Modules or cartridges, as they are commonly called, are emulated by a subsystem that emulates the ROMs, GROMs, and RAM in the cartridge. The contents of the cartridge ROM is stored as memory dump files in a package file which is actually a ZIP container. ROM and GROM contents are stored in separate files in this container. The container (which we call RPK container for ROM Package container) also contains an XML-formatted file which declares which file shall be associated with ROM or GROM space.
If the cartridge contains persistent RAM (like MiniMemory) which is not cleared when the computer is turned off, the contents are stored in nvram files, handled by the MAME/MESS core. As for now, there is no way to store these nvram contents in the RPK file, so you have to take care of these files by yourself (e.g. when you want to send the contents to someone else you have to check the nvram file).
Working with MiniMemory
MESS versions 0.126 to 0.131
When you want to use the Mini Memory NVRAM, you have to mount a pseudo module besides the Mini Memory GROM and ROM. This pseudo module must have a name ending in *m.bin, like memorym.bin. When you save a program using SAVE MINIMEM, a file is created in the nvram/ti99_4x subdiretory which corresponds to this pseudo file. That is, you can choose different NVRAM buffer files by selecting another pseudo RAM file. Note that the pseudo file itself is loaded but not transferred to memory.
MESS versions 0.132 and later
When the MiniMemory RPK is plugged in, the emulator automatically creates the NVRAM file. The name of the NVRAM file is determined in the layout.xml file in the RPK, so you can create different instances of the MiniMemory cartridge by choosing different NVRAM names.
To instantly clear the NVRAM, just delete the NVRAM file.