Memory Mapper Segment availability/allocation under MSXDOS/Nextor

All is described here: http://map.grauw.nl/resources/dos2_environment.php#c5

Note that the mapper support routines are a MSX-DOS2 function, although there is a TSR (MU.COM) which can also add mapper support to DOS1.

Also note that it is your responsibility to restore the slot and mapper page configuration to its initial state when your program terminates, also when it terminates abnormally. Unfortunately DOS doesn’t do this automatically, and if you don’t do it yourself the memory environment can get messed up causing bugs for programs that are run afterwards. The only thing that DOS does for you automatically on program termination is to free the user segments that you’ve allocated, though I think it’s good practice to also free these manually (for MU.COM support this is also mandatory).

As an additional note, be aware that MSX-DOS2 can load directly to the primary mapper only. So when you want to transfer data from disk to a non-primary mapper slot using the DOS calls, always use a buffer in between.

More precisely, Mapper support routines are a Disk-ROM v2.xx function. The function is present without booting under DOS2.

@gdx I presume you mean when executing in the BIOS/BASIC environment? Or do you mean to say that even think when booting in "DOS1 mode", with a key pressed at start-up or booting from a DOS1-formatted disk, these mapper support routines are available? (That would be novel to me.)

@DarkSchneider You can call the Extended BIOS from the BIOS/BASIC environment just as well as from the DOS environment (just like the BDOS functions can be called from both environments)... Nowhere have I ever read that the extended BIOS mapper routines are only supposed to be used in the DOS2 runtime environment, and I don’t see why that would be so either…

You access it in exactly the same way in both environments, calling the "Get mapper support routine address" routine on the EXTBIO entry point. This entry point is standard and not dependent on the DOS runtime. The only coupling to MSX-DOS2 is that it is included as part of the DiskROM v2.0, otherwise it is a completely independent system.